Light Emitting Device, Lighting System, Backlight Unit for Display Device and Display Device

ABSTRACT

To enhance emission efficiency and color rendering, a light emitting device  1  comprises: at least one light source  3 ; at least one first emitting section  4  having at least one sort of luminescent material that can emit light including a wavelength component that is longer than the light emitted from light source  3  when excited by the light emitted from light source  3 ; at least one second emitting section  5  having at least one sort of luminescent material that can emit light including a wavelength component that is longer than the light emitted from first emitting section  4  when excited by the light emitted from light source  3  and first emitting section  4 ; wherein light emitting device  1  comprises at least one light shielding unit  6  that protects at least a part of the light emitted from first emitting section  4  from entering second emitting section  5.

This application is a Continuation of U.S. Ser. No. 11/631,388 filed May14, 2007, allowed, which is a 371 application of PCT/JP05/11940 filedJun. 29, 2005 and claims the benefit of Japanese Application No.2004-194154 filed Jun. 30, 2004 and Japanese Application No. 2004-303363filed Oct. 18, 2004. The contents of each of these applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates to alight emitting device, a lighting system, abacklight unit for display device and a display device.

BACKGROUND ART

Devices such as cold cathode tube and the like have previously been usedas light source for a lighting system or a liquid crystal displaybacklight. Recently, pseudo-white light sources have been developed asan alternative light source, which is a combination of a light sourceemitting blue light and materials emitting yellow light as a result ofabsorbing blue light. In this pseudo-white light source, an InGaN baselight-emitting diode is used as light source emitting blue light andcerium-activated yttrium aluminate is used as a material emitting yellowlight, for example.

However, color spectrum generated by pseudo-white light sources isessentially deficient in green light component and red light componentand, therefore, these pseudo-white light sources were poor in theircolor rendering and color reproduction property. In order to solve thisproblem, proposals have been made to improve the light renderingproperty and light reproduction property of these pseudo-white lightsources. These proposals include modification of yttrium aluminatecomplex so that it emits yellowish green light, or further addition ofsuch substances as to absorb blue light and emit red light to theyttrium aluminate complex so as to supplement red light component of thepseudo-white light source.

In many cases, however, red luminescent materials absorb not only bluelight but also green light or yellow light whose wavelength is longerthan blue light but shorter than red light. As such substances can becited europium activated alkali earth metal sulfides, europium activatedalkali earth metal and silicon nitrides, and europium activated alkaliearth metal and silicon oxynitrides. These substances usually absorblight of 400 nm to 580 nm wavelength efficiently and emit orange to redlight with peak wavelength of 580 nm to 680 nm.

Orange to red luminescent materials, typified by the above-mentionedones, absorb shorter wavelength, green to yellow light. Therefore,combined use of orange to red luminescent materials and green to yellowluminescent materials results in partial absorption of green to yellowlight component by orange to red luminescent materials, and this causesa marked decrease in luminous flux of light emitting device.

At present, attempts are being made to prevent the loss of luminous fluxcaused by absorption of short wavelength light by luminescent materialsemitting long wavelength light. Patent Document 1 is one of suchexamples. In this patent, a light emitting device comprises two kinds ofmaterials (here called, “material A” and “material B”), which absorblight from a light source and emit light of different wavelength. It isso arranged that, when the material A (which corresponds to a materialemitting orange to red light) absorbs a part of the light emitted fromthe material B (which corresponds to a material emitting green to yellowlight), the improvement in color rendering and the prevention ofluminous flux loss can be achieved by locating the material A closer tothe light source than the material B is.

In addition, display devices have previously been used which visualizeclearly images formed on the image formation unit by irradiating light(backlight) directed against the image formation unit, with some imagesformed thereon, from behind. Display devices of this kind include:liquid crystal display using a liquid crystal unit as image formationunit, indoors indicator (emergency exit lamp, traffic signal and thelike) with its sign (image formation unit) illuminated with lightoriginated inside.

These display devices usually comprise a backlight unit which radiateslight from behind against the image formation unit. Fluorescence lampand cold cathode tube have previously been used as this kind ofbacklight unit.

The problem is, fluorescent lamps and cold cathode tubes, used asbacklight unit, are difficult to reduce in size of the backlight unitand., besides, their lifetime is rather short.

Another concern is that these devices contain mercury in them, which mayexert an undesirable effect on the environment, making their use evenmore difficult.

In recent years, a proposal has been made to design, as backlight unit,a light emitting device which makes use of a light source andfluorescent materials capable of absorbing light from the light sourceand emitting fluorescence. For example, the art as mentioned above,which utilizes pseudo-white light source as backlight unit usinglight-emitting diode of InGaN system and cerium-activated yttriumaluminate as light source and luminescent materials, respectively.

Another proposal is to use a light emitting device proposed in PatentDocument 1 as backlight.

[Patent Document 1] Japanese Patent Laid-Open Publication (Kokai) No.2004-71726

DISCLOSURE OF THE INVENTION Problem to Be Solved by the Invention

However, in the art of Patent Document 1, material A and material B emitlight in wide directions and a considerable portion of light emittedfrom material B (approximately half of it) is absorbed by material A,this causing marked loss of luminous flux. Emission efficiency of thislight emitting device was, therefore, low.

As was pointed earlier, a light emitting device comprising a lightsource emitting blue light and materials absorbing blue light andemitting yellow light achieves high emission efficiency but with poorcolor rendering.

In display devices based on previous light emitting devices, in order todisplay the color of images formed on the image formation unit with highcolor reproduction (that is, in order to enhance the colorreproduction), it is desirable that white light used as backlight islight containing three primary colors. Three primary colors hererepresent red, blue and green colors. From this standpoint, lightemitting devices, previously used and based on a light source emittingblue light and fluorescent materials emitting yellow light, aredeficient in red and green light components and their color reproductionis not adequate.

In a display device based on technology described in Patent Document 1,white light comprising all of blue, green and red light is emitted and,therefore, there is no problem in color reproduction. However, lightfrom fluorescent materials (red and green light) is emitted in widedirections and most of light emitted from green fluorescent materials isabsorbed by red fluorescent materials, causing marked loss in luminousflux. This leads to low emission efficiency of backlight unit and, also,to increased energy consumption of the display device.

The present invention has been made in view of such problems asmentioned above. The object of the invention includes the following: toheighten the emission efficiency and color rendering of a light emittingdevice which comprises two or more luminescent materials that absorb andemit light; to provide a lighting system, a backlight unit for a displaydevice and a display device, using the light emitting device; to providedisplay device with excellent color rendering property, by using abacklight unit with high emission efficiency.

Means for Solving the Problem

The inventors of the present invention made an intensive investigationto solve the above problems, and found that, with a light emittingdevice comprising two or more luminescent materials, it is possible toenhance the emission efficiency and color rendering of the lightemitting device by blocking the light from one luminescent material fromentering the region containing the other luminescent material, and thusby reducing the absorption amount of light emitted by one luminescentmaterial, by the other luminescent material.

On the basis of the above findings, a display device using backlight wasset up so that the backlight unit was composed of blue color lightsource emitting blue light, green light emitting section that containsgreen luminescent material emitting light on excitation by blue lightand that emits green light, and red light emitting section that containsred luminescent material emitting light on excitation by blue light andthat emits red light. The above green light emitting section and the redlight emitting section were arranged so that each unit, at least a partof them, can function independently. This resulted in the increase inemission efficiency of the white light emitted and improvement in colorrendering property of the display device, leading to the completion ofthe present invention.

Accordingly, the light emitting device of the present invention ischaracterized in that it comprises: at least one light source; at leastone first emitting section having at least one sort of luminescentmaterial that can emit light including a wavelength component that islonger than that of the light emitted from said light source whenexcited by the light emitted from said light source; at least one secondemitting section having at least one sort of luminescent material thatcan emit light including a wavelength component that is longer than thatof the light emitted from said first emitting section when excited bythe light emitted from said light source and said first emittingsection; and at least one light shielding unit that protects at least apart of the light emitted from said first emitting section from enteringsaid second emitting section (claim 1). With this construction, theabsorption of light coming from the first emitting section by the secondemitting section is reduced, and, as a consequence, emission efficiencyand color rendering of the light emitting device can be improved.

It is desirable that said light shielding unit reflects at least a partof the light emitted from said first emitting section (claim 2). Thismakes possible the efficient use of light emitted from the firstemitting section and improves the emission efficiency and colorrendering of the light emitting device.

The lighting system of the present invention is characterized by the useof the above-mentioned light emitting device (claim 3).

Further, the backlight unit for display device of the present inventionis characterized by the use of the above-mentioned light emitting device(claim 4).

Further, the display device of the present invention is characterized bythe use of the above-mentioned light emitting device (claim 5).

Another display device of the present invention is characterized in thatit comprises: at least one backlight unit that emits backlight; and atleast one image formation unit that forms images at the front sidethereof when irradiated with the backlight emitted by said backlightunit on the back side thereof; wherein said backlight unit comprises: atleast one light source; at least one first emitting section having atleast one sort of luminescent material that can emit light including awavelength component that is longer than that of the light emitted fromsaid light source when excited by the light emitted from said lightsource; and at least one second emitting section formed at least partlyindependently of said first emitting section and having at least onesort of luminescent material that can emit light including a wavelengthcomponent that is longer than that of the light emitted from said firstemitting section when excited by the light emitted from said lightsource and said first emitting section. (Claim 6). With thisconstruction, both emission efficiency and color rendering property ofthe display device can be improved.

As another preferred feature of the present invention, the displaydevice comprises: at least one backlight unit that emits white light;and at least one image formation unit that forms images at the frontside thereof when irradiated with the white light emitted by saidbacklight unit on the back side thereof; wherein said backlight unitcomprises: at least one blue color light source that emits blue light;at least one green light emitting section having green luminescentmaterial that emits green light when excited by the blue light so as toemit green light; and at least one red light emitting section, formed atleast partly independently of said green light emitting section, havingred luminescent material that emits red light when excited by the bluelight so as to emit red light (claim 7). Also with this construction,both emission efficiency and color rendering property of the displaydevice can be improved.

It is preferred that the display device mentioned above comprises atleast one diffusion plate, placed between said backlight unit and saidimage formation unit, so as to disperse the light emitted from saidbacklight unit (claim 8).

It is also preferred that the display device mentioned above comprisesat least one optical waveguide so as to lead the light from saidbacklight unit to said image formation unit (claim 9).

Advantageous effect of the invention

The present invention makes possible the creation of a light emittingdevice which is excellent in both emission efficiency and colorrendering.

The use of the light emitting device of the present invention makespossible the creation of a lighting system, backlight unit for displaydevice, and display device which is excellent in both emissionefficiency and color rendering.

Further, both emission efficiency and color reproduction property of adisplay device can be greatly improved through the use of the displaydevice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) and FIG. 1( b) show schematically the essential part of alight emitting device, as exemplified in a first embodiment of thepresent invention. FIG. 1( a) is its cross-sectional view and FIG. 1( b)is its exploded perspective view.

FIG. 2( a) and FIG. 2( b) show schematically the essential part of alight emitting device, as exemplified in a second embodiment of thepresent invention. FIG. 2( a) is its cross-sectional view and FIG. 2( b)is its exploded perspective view.

FIG. 3 is a schematic cross-sectional view of the essential part of adisplay illustrating one example of a backlight unit using a lightemitting device of the present invention.

FIG. 4 is a schematic, exploded perspective view illustrating theoutline of a display device, as exemplified in a third embodiment of thepresent invention.

FIG. 5 is a schematic plane view of a backlight unit, as exemplified ina third embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view illustrating the essentialpart of a backlight unit, as exemplified in a third embodiment of thepresent invention.

FIG. 7 is a chromaticity diagram illustrating the desirable range of thechromaticity coordinates of light generated by mixing blue light andgreen light, as exemplified in the display unit of a third embodiment ofthe present invention.

FIG. 8 is a schematic cross-sectional view illustrating the essentialpart of a backlight unit, as exemplified in the modified example of athird embodiment of the present invention.

FIG. 9 is a schematic, cross-sectional view of one example of theconstitution of a light emitting section using a surface-mounted typeframe, as exemplified in the backlight unit in the modified example of athird embodiment of the present invention.

FIG. 10 is a schematic cross-sectional view illustrating theconstitution of a display device using a optical waveguide, asexemplified in the modified example of a third embodiment of the presentinvention.

FIG. 11 is a chromaticity diagram illustrating the method of generatingwhite light, as explained in examples 1 to 4 of the present invention.

FIG. 12 is a graph showing the emission spectrum of white light, ascalculated for example 1 of the present invention.

FIG. 13 is a graph showing the emission spectrum of white light, ascalculated for example 2 of the present invention.

FIG. 14 is a graph showing the emission spectrum of white light, ascalculated for example 3 of the present invention.

FIG. 15 is a graph showing the emission spectrum of white light, ascalculated for example 4 of the present invention.

FIG. 16 is a chromaticity diagram illustrating the method of generatingwhite light, as explained in examples 5 to 7 of the present invention.

FIG. 17 is a graph showing the emission spectrum of white light, ascalculated for example 5 of the present invention.

FIG. 18 is a graph showing the emission spectrum of white light, ascalculated for example 6 of the present invention.

FIG. 19 is a graph showing the emission spectrum of white light, ascalculated for example 7 of the present invention.

FIG. 20 is a chromaticity diagram illustrating the method of generatingwhite light, as explained in examples 8 to 11 of the present invention.

FIG. 21 is a graph showing the emission spectrum of white light, ascalculated for example 8 of the present invention.

FIG. 22 is a graph showing the emission spectrum of white light, ascalculated for example 9 of the present invention.

FIG. 23 is a graph showing the emission spectrum of white light, ascalculated for example 10 of the present invention.

FIG. 24 is a graph showing the emission spectrum of white light, ascalculated for example 11 of the present invention.

FIG. 25 is a chromaticity diagram illustrating the method of generatingwhite light, as explained in examples 12 to 14 of the present invention.

FIG. 26 is a graph showing the emission spectrum of white light, ascalculated for example 12 of the present invention.

FIG. 27 is a graph showing the emission spectrum of white light, ascalculated for example 13 of the present invention.

FIG. 28 is a graph showing the emission spectrum of white light, ascalculated for example 14 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be explained in detail referring toexamples. It should be borne in mind that the present invention is notlimited to the below-described examples and can be modified any wayinsofar as it does not depart from the scope of the invention.

I. Explanation on Light Emitting Device I-1. Summary of Light EmittingDevice

A light emitting device of the present invention is equipped with alight source, the first emitting section, the second emitting sectionand a light shielding unit, and is designed to emit light in thedesired, predetermined direction (hereinafter referred to as“predetermined direction”, as needed). Usually, the light emittingdevice has a frame which functions as a base to hold the light source,the first emitting section, the second emitting section and the lightshielding unit.

I-1-1. Frame

The frame is a base to hold the light source, the first emittingsection, the second emitting section and the light shielding unit, andno special limitation is imposed on its shape and its material.

As for specific examples of the frame shape, it can take any form suchas board or cup, to cite a few, depending on its use. Among them, acup-shaped frame is preferable because it can emit light in the desireddirection, making possible the efficient use of light emitted from thelight emitting device.

Various materials can be used to make a frame. They include inorganicmaterials such as metal, alloy, glass, carbon or ceramics, and organicmaterials such as synthetic resin. An appropriate one can be selectedaccording to the method the frame is used.

Further, it is preferable to use for a frame material capable ofliberating heat, for example, a material with high thermal conductivity.Usually, a light source releases heat during its use. A frame with agood heat liberation property assures its stable and continuous use evenif heat is released during its use.

Furthermore, it is preferable to use, for a frame, a material with goodelectrical insulation property.

At this point, it is preferable that a surface of the frame, irradiatedwith light emitted from the light source, the first emitting section andthe second emitting section, has a heightened reflectance with regard toat least some component of the irradiated light. It is more preferablethat the reflectance is heightened for all the wavelength region ofvisible light. Therefore, it is preferable that at least a surface ofthe frame irradiated with light is made of material having highreflectance. Examples include materials (resin used for injectionmolding and the like) containing substances of high reflectance, such asglass fiber, alumina powder or titania powder. It is preferable to makethe entire frame, or the surface of the frame, with such materials.

There is no special limitation on the method to increase the reflectanceof the surface of a frame. In addition to selecting a suitable materialfor the frame itself as described above, it is possible to heighten thelight reflectance by plating or evaporation-coating the frame with metalor alloy having high reflectance, such as silver, platinum or aluminum.

Enhanced light reflection can be provided to only a part of the frame orto the entire frame. It is preferable that all the surfaces irradiatedwith light from the light source, the first emitting section and thesecond emitting section have enhanced light reflectance.

Additionally, a frame has usually an electrode via which electric poweris supplied to the light source.

I-1-2. Light Source

A light source emits exciting light capable of exciting luminescentmaterials contained in the first emitting section and the secondemitting section. It also emits light constituting one component oflight emitted from the light emitting device. In other words, a part oflight from the light source is absorbed by luminescent materials of thefirst and the second emitting sections as exciting light, and anotherpart is emitted from the light emitting device in the predetermineddirection.

As light source can be used any kind of light source, depending on theuse and constitution of the light emitting device. Examples of the lightsource include: light emitting diode (hereinafter, if necessary, called

“LED”), edge-emitting or surface emitting laser diode,electroluminescence element or the like. Usually, inexpensive LED ispreferable.

There is no special limitation on the wavelength of light emitted by thelight source. Any light source capable of emitting light of suitablewavelength may be selected, depending on the light intended to beemitted from the light emitting device. When white light is intended tobe emitted from the light emitting device, for example, the wavelengthof light from the light source is usually 370 nm or higher, preferably380 nm or higher, and usually 500 nm or lower, preferably 480 nm orlower.

As specific examples of light source can be cited LED based onsemiconductors of InGaN system, GaAlN system, InGaAlN system or ZnSeSsystem with crystals grown on a baseboard such as silicon carbide,sapphire or gallium nitride by the MOCVD method and the like.

It is to be noted that one light source can be used singly, or two ormore light sources can be used together. Also, one kind of light sourcecan be used, or two or more kinds can be used together. In particular,it is preferable to use a separate light source for each of the firstemitting section and the second emitting section to enhance the colorrendering of the light emitting device.

In case a common light source is installed for the first emittingsection and the second emitting section, instead of installing aseparate, independent light source for each section, it is preferable toposition the first emitting section closer to the light source than thesecond emitting section. In other words, the shortest distance betweenthe light source and the first emitting section is preferably smallerthan the shortest distance between the light source and the secondemitting section.

Suppose that a light shielding unit blocks only a part of the lightbetween the first emitting section and the second emitting section andthat a light source is placed closer to the second emitting section thanthe first emitting section and the light emitted from the light sourcefirst enters the second emitting section. In that case, the secondemitting section emits light on receiving light from the light source asexciting light. As the light thus emitted can not be used as excitinglight of the first emitting section, light from the first emittingsection may be deficient in intensity or light from the second emittingsection may be too strong in intensity. This may result in thefluctuation of the components of light emitted by the light emittingdevice from the intended value, and leads to the lowering of colorrendering. On the other hand, if the first emitting section is placedcloser to the light source than the second emitting section, the lightfrom the light source first enters the first emitting section, which isexcited by that light and, as a result, emits light. In this way, boththe first emitting section and the second emitting section can performtheir emitting function as intended. This will result in littlefluctuation of color components of the light emitted from the lightemitting device and hence, promote color rendering further.

Even when the first emitting section is placed closer to the lightsource than the second emitting section, the intensity of the lightentering the two sections is also related to other factors such as thesurface area, where is irradiated with light from the light source, ofthe two light emitting sections. Therefore, the distance between thelight source and each light emitting section, and the surface area ofthe two light emitting sections should be designed so that the intensityof the light from the light source at the first emitting section isgreater than that at the second emitting section.

There is no special limitation on the method by which a light source isattached to a frame. Soldering is one such method. The kind of solder isnot limited to any special one. For example, AuSn or AgSn can be used.In case it is attached by soldering, it is possible to supply electricpower from an electrode, formed on the frame, via solder. Especiallywhen high power LED or laser diode, in which the heat release matters,is used as light source, soldering is particularly useful because of itsexcellent heat dissipating property.

In case a method other than soldering is to be used to attach a lightsource to a frame, an adhesive agent such as epoxy resin, imide resin oracrylic resin can be used, for example. In this case, use can be made ofa paste prepared by adding electroconductive filler such as silverparticles or carbon particles to the adhesive agent, which makespossible the electric power supply to the light source by energizing theadhesive agent, similarly to when soldering is used. The use ofelectroconductive filler is desirable also from the viewpoint ofincreasing heat dissipating property.

Electric power can be supplied to a light source by any method. Inaddition to the above-mentioned methods via solder or adhesive agents, alight source and electrode can be connected by wire bonding. There is nolimitation on the material or the size of the wire. For example, metalssuch as gold or aluminum can be used as materials and its diameter isusually in the range of 20 μm to 40 μm. The material or the size,however, is by no means limited by these examples.

As another example of the method of supplying electric power to a lightsource can be cited a method based on flip-chip mounting using a bump.

I-1-3. First Emitting Section and Second Emitting Section

The first emitting section is constructed to comprise at least one sortof luminescent material which is excited by light from a light sourceand emits light including a longer wavelength component than the lightfrom the light source. There is no special limitation on the shape ofthe first emitting section. It can be installed as a single unit in onelocation, or as two or more units in more than one location. Luminescentmaterials used in the first emitting section will be described in detaillater.

The first emitting section receives light from a light source asexciting light and, as a result, light is emitted by luminescentmaterials. Light emitted from the first emitting section constitutes acomponent of light emitted outside from the light emitting device. Incase a light shielding unit prevents only a part of the light emittedfrom the first emitting section from entering the second emittingsection, a part of light from the first emitting section functions asexciting light of the luminescent materials in the second emittingsection.

The second emitting section, on the other hand, is constructed tocomprise at least one luminescent material which is excited by lightfrom a light source and also from the first emitting section and emitlight containing longer wavelength component than light from the firstemitting section. There is no special limitation on the shape of thesecond emitting section. It can be installed as a single unit in onelocation, or as two or more units in more than one location. Luminescentmaterials used in the second emitting section will be described indetail later.

The second emitting section receives light from a light source asexciting light and, as a result, light is emitted by luminescentmaterials. In case the second emitting section receives light from thefirst emitting section, this light also serves as exciting light,causing the luminescent materials to emit light. Light thus emitted fromthe second emitting section constitutes a component of light emittedoutside from the light emitting device.

Furthermore, it is desirable that the first emitting section and thesecond emitting section mentioned above are opened to the outside of thedevice at their light exit side. The light exit side referred to hereindicates a surface from which the light emitting device emits light inthe predetermined direction. Accordingly, light emitted from lightsource, the first emitting section and the second emitting section isemitted from this light exit side in the predetermined direction. Thereis no limitation on the shape of the light exit side. Depending on theuse of the device, a flat surface, curved surface, concavo-convexsurface or the like may be selected. When the light emitted from thelight emitting device is emitted in more than one direction, or emittedradially within a certain angle, it is usually so arranged that thestrongest light is emitted in the predetermined direction.

That the first emitting section and the second emitting section areopened indicates that the light emitted from these sections in thepredetermined direction is not blocked by other members. Moreconcretely, light emitted from the first emitting section in thepredetermined direction is emitted to the outside of the light emittingdevice without being blocked by the light source, light shielding unit,the second emitting section and the frame (if the device is fitted witha frame). Likewise, light emitted from the second emitting section inthe predetermined direction is emitted to the outside of the lightemitting device without being blocked by the light source, lightshielding unit, the first emitting section and the frame (if the deviceis fitted with a frame). Even in case there is a protective layer formedon the light exit side, or there is a cover placed on the light emittingdevice, and light emitted from the first emitting section and the secondemitting section must pass through these members before leaving thelight emitting device, the first emitting section and the secondemitting section are deemed opened if the protective layer, cover or thelike is such that they allow the light to pass through.

As described above, the first emitting section and the second emittingsection, opened at their light exit side, assures that the decrease inintensity of the light emitted from these first and second emittingsections, by making the light be absorbed in the other luminescentmaterial or blocked by the other members, is kept small (or none atall). This can lead to the increase in emission efficiency, decrease influctuation of light components emitted from the light emitting device,and improvement in color rendering. That the light of three primarycolors, blue, red and green, can be emitted from the light emittingdevice ensures excellent color reproduction property, subject to properselection of the light source, the first emitting section and the secondemitting section.

I-1-4. Light Shielding Unit

The function of the light shielding unit is to prevent the light emittedfrom the first emitting section from entering the second emittingsection. At least, a part of light emitted by the first emitting sectionmust be blocked from entering the second emitting section by this lightshielding unit. Usually, light from the first emitting section should beblocked from entering the second emitting section to the extent thatlight emitted from the light emitting device has sufficiently highemission efficiency and color rendering to make the device practicallyusable. It is more preferable that all the light from the first emittingsection is prevented from entering the second emitting section. In thisway, light from the first emitting section can be blocked from beingconsumed as exciting light of the second emitting section. Decrease inlight intensity of the first emitting section can thus be prevented,leading to an improvement in emission efficiency and color rendering ofthe light emitting device.

Furthermore, it is preferable that the light shielding unit is sodesigned as to reflect at least a part of the light emitted by the firstemitting section. It is more preferable that the light shielding unit isso designed as to reflect all the light which is emitted by the firstemitting section and is irradiated on the light shielding unit. Thisconstruction makes possible the efficient use of the light from thefirst emitting section, leading to enhanced emission efficiency andcolor rendering of the light emitting device.

In this connection, it is also preferable that the light shielding unitis so designed as to reflect at least a part of the light emitted by thesecond emitting section. It is more preferable that the light shieldingunit is so designed as to reflect all the light which is emitted by thesecond emitting section and is irradiated on the shielding unit. Thisconstruction makes possible the efficient use of the light from thesecond emitting section, leading to enhanced emission efficiency andcolor rendering of the light emitting device.

Furthermore, it is preferable that the light shielding unit is sodesigned as to reflect at least a part of the light emitted by the lightsource. It is more preferable that the light shielding unit is sodesigned as to reflect all the light which is emitted by the lightsource and is irradiated on the shielding unit. This construction makespossible the efficient use of the light from the light source, leadingto enhanced emission efficiency and color rendering of the lightemitting device.

In concrete terms, it is preferable that at least a part of the surfaceof the light shielding unit has a high reflectance for at least somecomponents of light irradiated on the light shielding unit (from eitherthe light source, the first emitting section or the second emittingsection). It is more preferable that it has a high reflectance for allthe wavelength range of visible light. Therefore, it is preferable that,like the frame, at least its surface, irradiated with light, is made ofmaterials having a high reflectance. As examples are cited materialscontaining high-reflectance substance like glass fiber, alumina powder,titanium powder and the like (for example, resin for injection molding).These materials can be used to manufacture the entire light shieldingunit or the surface of the light shielding unit.

There is no special limitation on the method used to increase thereflectance of the surface of the light shielding unit. In addition tothe selective use of the materials constituting the light shielding unititself, as described above, it is possible to plate the unit with suchmetals as silver, platinum, aluminum or with alloys, which has highreflectance.

The surface with enhanced light reflectance can be the entire surface ofthe light shielding unit or a part thereof. Usually, it is preferredthat the entire surface, irradiated with light from the light source,the first emitting section and the second emitting section has highreflectance.

There is no special limitation on the shape of the light shielding unitprovided that it is capable of blocking at least a part of the lightfrom the first emitting section from reaching the second emittingsection. It can be shaped in the form of plate, net or mesh, placedbetween the first emitting section and the second emitting section.Further, the light shielding unit may be formed integrated with theframe, or separately therefrom. It is usually preferable, though, todecide the position of the light shielding unit so that the lightemitting device can emit the intended light efficiently, taking intoconsideration the emission intensity of the first emitting section andthe second emitting section.

It is preferred that a plurality of concave portions (such as cup-shapedrecessions) is formed on the frame and each concave portion has thelight source and the first or second emitting section, in the viewpointof ease in production of the light emitting device. In this instance,each wall separating adjacent concave portions functions as lightshielding unit. The display device having this constitution will bedescribed in detail in the third embodiment.

There is no specific restriction on the material of light shieldingunit, insofar as it can prevent at least a part of light from the firstemitting section from entering the second emitting section. It mayinclude inorganic materials such as metal, alloy or glass, and organicmaterials such as synthetic resin or carbon. An appropriate one can beselected according to the manner the unit is used. In particular,usually, a material that reflects and does not absorb the light from thefirst and second emitting sections, like described above, is preferablyused.

In the light emitting device of the present invention, there provided alight shielding unit between the first and second emitting sections.This construction makes it possible to prevent the light emitted fromthe first emitting section from entering the second emitting section.This improves the emission efficiency and color rendering of the lightemitting device. The explanation about this mechanism will be made inthe following section.

Previously, when a part of the light is emitted from the first emittingsection toward the second emitting section, the light enters the secondemitting section and the luminescent material of the second emittingsection absorbs the light from the first emitting section as excitinglight. This means there occurs the consumption of the light emitted fromthe first emitting section by the second emitting section. Therefore,the intensity of the light from the first emitting section, intended toemerge outside of the light emitting device, gets lowered, leading todecrease in luminous flux of the light emerging from the light emittingdevice and thus in emission efficiency. In addition, as the lightemitted from the first emitting section is consumed by the secondemitting section, optical component balance of the light emerging fromthe light emitting device is fluctuated, leading to decrease in colorreproduction of the light emitting device.

Moreover, in the conventional construction like Patent Document 1, it isnecessary to enlarge the ratio of the luminescent material in the firstemitting section against that in the second emitting section to obtain adesired color of the light emerging from the light emitting device,because of the compensation of light emitted from the first emittingsection and absorbed in the second emitting section. However, colorrendering of light emerging from the light emitting device depends onkinds and usage ratio of luminescent material. That is why the colorrendering of the light has been liable to get insufficient, becauseusage ratio of luminescent material tends to drop out the optimal valuevery far in the conventionally constructed light emitting device likePatent Document 1.

In contrast to this, in the light emitting device of the presentinvention, the light shielding unit prevents light from the firstemitting section from reaching the second emitting section. This leadsto the protection of decrease in intensity of light emitted from thefirst emitting section and absorbed by the second emitting section.Consequently, emission efficiency of the light emitting device can beenhanced compared to the conventional one.

In addition, as the second emitting section can be prevented fromabsorbing light from the first emitting section and emitting light,fluctuation in optical component of the light from the light emittingdevice can be lowered. This leads to enhanced color rendering of thelight emitting device, resulting in also improved color rendering andcolor reproduction property of the light emitting device.

The position, dimensions, shape or the like of components constitutingthe light emitting device may be decided arbitrarily, insofar as someexciting light (mainly, the light form the light source) can be appliedto the first and the second emitting section and light emitted from thelight source, first emitting section and second emitting section canemerge outside of the light emitting device.

For example, the first emitting section, second emitting section, lightsource and frame can be positioned apart from each, having a gap betweeneach. As a specific example, there may be provided a gap between thefirst emitting section and second emitting section. As another example,there may be a gap between both or either of the first and secondemitting sections and light source. As still another example, there maybe a gap between both or either of the first and second emittingsections and light shielding unit.

Further, in case some distance is put between the first and secondemitting sections, or between either or both of the first and secondemitting sections and the light source, for them not to touch with each,some other members may be provided between them. At this point, it ispreferable to use desired-light-permeable materials, such as glass orresins like epoxy resin or silicone resin, as other members, becausethey can maintain luminous flux to be high. As an specific example, acover layer made of transparent resin can be formed on allcircumferences of the light source. Although the first and secondemitting sections are separated with this cover layer, light from thelight source can be applied to the first and second emitting sectionssurely as exciting light in a state where the luminous flux is kept tobe high. This makes it possible to protect the light source, withoutlowering intensity of the light emerging from the light emitting device.

In addition, the sizes of the first and the second emitting sections maydiffer, as mentioned above.

Also, the light emitting device of the present invention may comprisemembers other than the above-mentioned light source, first emittingsection, second emitting section and frame.

For example, it may comprise a cover for protecting the light emittingdevice itself.

For another example, it may comprise a light guide member, such asmirror, prism, lens, optical fiber or the like, for changing thedirection in which light emerges from the light emitting device.

It may also comprise a heat dissipation plate for releasing heatgenerated in the light emitting device.

It may further comprise, for example, a light diffusion layer or thelike outside the light exit side of the light emitting device, fordiffusing each component of the light emerging from the light emittingdevice so as to prevent the color irregularity of the light perceivedvisually.

I-2. Composition of Light Emitting Section

Luminescent materials used in the light emitting device of the presentinvention can be any substances capable of absorbing excitation lightand emitting light containing longer wavelength components than theabsorbed exciting light. Luminescent materials are usually mixed withbinders when used to form the first emitting section and the secondemitting section.

I-2-1. Luminescent Materials

Luminescent materials can be selected from any known such substances,depending on the manner the light emitting devices are used. Lightemission can be through any mechanism including fluorescence orphosphorescence. In the first emitting section as well as in the secondemitting section, luminescent materials can be either a single sort ofsubstance or a mixture of more than one sort of substances in anypossible combination or in any possible ratio. However, luminescentmaterials in the first emitting section should be selected from thoseemitting light containing longer wavelength components than the lightemitted by the light source, when excited by light from the lightsource. Luminescent materials in the second emitting section should beselected from those emitting light containing longer wavelengthcomponents than the light emitted by the first emitting section, whenexcited by light from the light source and the first emitting section.

As luminescent materials are preferred those substances absorbingexcitation light at wavelength of usually 350 nm or longer, preferably400 nm or longer, more preferably 430 nm or longer, and absorbingexcitation light at wavelength of usually 600 nm or shorter, preferably570 nm or shorter, more preferably 550 nm or shorter.

Furthermore, luminescent materials are preferably those substancesemitting light at wavelength of usually 400 nm or longer, preferably 450nm or longer, more preferably 500 nm or longer, and emitting light atwavelength of usually 750 nm or shorter, preferably 700 nm or shorter,more preferably 670 nm or shorter.

Regarding luminescent materials of the first emitting section inparticular, it is preferable to use those substances absorbingexcitation light at wavelength of usually 350 nm or longer, preferably400 nm or longer, more preferably 430 nm or longer, and absorbing lightat wavelength of usually 520 nm or shorter, preferably than 500 nm orshorter, more preferably 480 nm or shorter.

Furthermore, luminescent materials of the first emitting section shouldbe those substances emitting light at wavelength of usually 400 nm orlonger, preferably 450 nm or longer, more preferably 500 nm or longer,and emitting light at wavelength of usually 600 nm or shorter,preferably 570 nm or shorter, more preferably 550 nm or shorter.

On the other hand, as luminescent materials of the second emittingsection are preferred those substances absorbing excitation light atwavelength of usually 400 nm or longer, preferably 450 nm or longer,more preferably 500 nm or longer, and absorbing light at wavelength ofusually 600 nm or shorter, preferably 570 nm or shorter, more preferably550 nm or shorter.

Furthermore, luminescent materials of the second emitting section arepreferably those substances emitting light at wavelength of usually 550nm or longer, preferably 580 nm or longer, more preferably 600 nm orlonger, and emitting light at wavelength of usually 750 nm or shorter,preferably 700 nm or shorter, more preferably 670 nm or shorter.

It is preferable to use luminescent materials having luminous efficiencyof usually 40% or longer, preferably 45% or longer, more preferably 50%or longer, still more preferably 55% or longer, most preferably 60% orlonger. The luminous efficiency mentioned here represents a product ofquantum absorbing efficiency and internal quantum efficiency.

In the following section, preferable luminescent materials to be used inthe light emitting device of the present invention will be explained, byexemplifying those suitable for each emitting section. It should benoted that luminescent materials are not limited to those exemplified inthe following section, and each substance can be used either for thefirst emitting section or for the second emitting section, within thescope of the present invention.

(Examples of Suitable Luminescent Materials of the First EmittingSection)

(First Example of the First Emitting Section)

As the first example of the suitable luminescent materials of the firstemitting section can be cited the phosphor described by the formula (1)below.

M¹ _(a)M² _(b)M³ _(c)O_(d)   Formula (1)

In the formula (1) above, M¹, M², and M³ represent a bivalent metalelement, a trivalent metal element, and a tetravalent metal element,respectively, and a, b, c, and d indicate values in the range shownbelow.

2.7≦a≦3.3

1.823 b≦2.2

2.7≦c≦3.3

11.0≦d≦13.0

In the formula (1) above, M¹ is a bivalent metal element. In view ofluminous efficiency or the like, it is preferably at least one type ofelement selected from the group consisting of Mg, Ca, Zn, Sr, Cd, andBa, more preferably one element selected from Mg, Ca, and Zn. Ca isparticularly preferable. In this instance, Ca can be used either singlyor in combination with Mg. In principle, M¹ should consist of theelements referred to above as preferable. However, it can contain otherbivalent metal elements, as far as efficiency is not impaired.

In the formula (1) above, M² is a trivalent metal element. As is thecase with M¹, it is preferably at least one type of element selectedfrom the group consisting of Al, Sc, Ga, Y, In, La, Gd, and Lu, morepreferably one element selected from Al, Sc, Y, and Lu. Sc isparticularly preferable. In this instance, Sc can be used either singlyor in combination with Y or Lu. In principle, M² should consist of theelements referred to above as preferable. However, it can contain othertrivalent metal elements, as far as efficiency is not impaired.

In the formula (1) above, M³ is a tetravalent metal element. From thesame consideration as for M¹ and M², it is preferable that M³ containsSi as a minimum requirement. The content of Si in M³ is usuallypreferably 50 mole % or more, more preferably 70 mole % or more, farmore preferably 80 mole % or more, most preferably 90 mole % or more.

In the formula (1) above, apart from Si, tetravalent M³ is preferably atleast one type of element selected from the group consisting of Ti, Ge,Zr, Sn and Hf, more preferably one element selected from Ti, Zr, Sn andHf. Of these, Sn is most preferred. The most preferred M³ element is Si.In principle, M³ should consist of the elements referred to above aspreferable. However, it can contain other tetravalent metal elements, asfar as efficiency is not impaired.

In this specification, efficiency is deemed not impaired if the contentof other elements, relative to above-mentioned M¹, M² and M³, is 10 mole% or lower, preferably 5 mole % or lower, more preferably 1 mole % orlower.

The crystal structures of the above-mentioned phosphors are usually oneof the garnet crystal structures. This is usually a body centered cubiclattice crystal where a, b, c and d in the formula (1) above representthe value of 3, 2, 3 and 12, respectively. However, in case where, forexample, the element constituting the luminescent center ion occupiesthe position of the crystal lattice of one of the metal ions of M¹, M²,and M³, or is located in the interstice, a, b, c and d may deviate fromthe above values, that is, 3, 2, 3 and 12. It is, therefore, preferredthat a, b, c and d falls within the following range: 2.7≦a3.3,1.8≦b≦2.2, 2.7≦c≦3.3 and 11.0≦d≦13.0.

The luminescent center ion, contained in the host material of theabove-mentioned crystal structure, is required to contain at least Ce.For the fine adjustment of its fluorescence property, it may contain atleast one type of divalent to tetravalent element selected from thegroup consisting of Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Sm, Eu, Tb, Dy, Ho,Er, Tm and Yb. Preferably, it contains at least one type of divalent totetravalent element selected from the group consisting of Mn, Fe, Co,Ni, Cu, Sm, Eu, Tb, Dy and Yb. Divalent Mn, divalent to trivalent Eu, ortrivalent Tb is particularly preferred to be used.

This phosphor is usually excited by light whose wavelength is in therange of 420 nm to 480 nm. The emission spectrum is in the range of 450nm to 650 nm with its peak in the range of 500 nm to 510 nm.

As concrete examples of the phosphor described above are citedCa₃Sc₂Si₃O₁₂:Ce, Ca₃(Sc,Mg)₂Si₃O₁₂:Ce etc.

(Second Example of the First Emitting Section)

As the second example of suitable luminescent materials of the firstemitting section can be cited the phosphors described by the formula (2)below.

M¹ _(a)M² _(b)M³ _(c)O_(d)   Formula (2)

In the formula (2) above, M¹ is an activating element that contains Ceas a minimum requirement, M² is a bivalent metal element, M³ is atrivalent metal element, and a, b, c and d indicate values in the rangeshown below.

0.0001≦a≦0.2

0.8≦b≦1.2

1.6≦c≦2.4

3.2≦d≦4.8

In the formula (2) above, M¹ represents an activating element containedin a host crystal referred to later, and contains Ce as a minimumrequirement. For the purpose of improving light storage property,chromaticity adjustment or intensification, it can contain at least onetype of divalent to tetravalent element selected from the groupconsisting of Cr, Mn, Fe, Co, Ni, Cu, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho,Er, Tm and Yb.

In the formula (2) above, a, which represents the content of activatingelement M¹, is a value in the range of 0.0001≦a≦0.2. In case the valueof a is too small, the number of the luminescent center ions in the hostcrystal of the phosphor is small and this may result in the lowering ofemission intensity. On the other hand, if the value of a is too large,concentration quenching may occur, resulting in the lowering of emissionintensity. In terms of emission intensity, therefore, the value of a ispreferably 0.0005 or larger. More preferably, it is 0.002 or larger. Onthe other hand, it is preferably 0.1 or smaller. More preferably, it is0.04 or smaller. As the content of Ce becomes higher, the emission peakwavelength is shifted to a longer wavelength region resulting in arelative increase in the emitting amount of green light component havinghigh visual sensitivity. Therefore, from the viewpoint of desirablebalance of emission intensity and emission peak wavelength, thepreferable value of a is usually 0.004 or larger. More preferably, it is0.008 or larger. Still more preferably, it is 0.02 or larger. On theother side, it is preferably 0.15 or smaller. More preferably, it is 0.1or smaller. Still more preferably, it is 0.08 or smaller.

In the formula (2) shown above, M² is a bivalent metal element. From thestandpoint of luminous efficiency, it is preferably at least one type ofelement selected from the group consisting of Mg, Ca, Zn, Sr, Cd and Ba,more preferably one element selected from Mg, Ca, and Sr. It isparticularly preferable that Ca accounts for 50 mole % or more of theelements of M².

In the formula (2) shown above, M³ is a trivalent metal element. Fromthe same consideration as for M², it is preferably at least one type ofelement selected from the group consisting of Al, Sc, Ga, Y, In, La, Gd,Yb and Lu, more preferably one element selected from Al, Sc, Yb and Lu.Far more preferable is Sc or a combination of Sc and Al or a combinationof Sc and Lu. It is particularly preferable that Sc accounts for 50 mole% or more of the elements of M³.

The host crystal of the above-mentioned phosphor is usually a crystalrepresented by the composition M²M³ ₂O₄, which consists of a divalentmetal element M², trivalent metal element M³ and oxygen. In terms ofchemical composition, therefore, b, c and d in the formula (2) aboveindicate a number of 1, 2 and 4, respectively. However, in case where,for example, the activating element Ce occupies the position of thecrystal lattice of the metal elements M² or M³, or is located in theinterstice, b, c and d may deviate from the above-mentioned values, thatis, 1, 2 and 4.

In the formula (2) above, b represents a value which is usually 0.8 orlarger, preferably 0.9 or larger. It is usually 1.2 or smaller,preferably 1.1 or smaller. And, c represents a value which is usually1.6 or larger, preferably 1.8 or larger. It is usually 2.4 or smaller,preferably 2.2 or smaller. Further, d represents a value which isusually 3.2 or larger, preferably 3.6 or larger. It is usually 4.8 orsmaller, preferably 4.4 or smaller.

In the formula (2) above, M² and M³ represent a divalent metal elementand a trivalent metal element, respectively. A very small amount of M²and/or M³ can be replaced by univalent, tetravalent or pentavalent metalelement so as to adjust the balance of the electric charge or the like,if that replacement does not cause any fundamental change in lightemitting characteristics or crystal structure of the phosphor. Further,the phosphor can also contain a minute amount of anions such as halogen(F, Cl, Br, I), nitrogen, sulfur or selenium.

This phosphor is excited by light whose wavelength is in the range of420 nm to 480 nm. The most efficient excitation range is 440 nm to 470nm. The emission spectrum is in the range of 450 nm to 700 nm with itspeak in the range of 490 nm to 550 nm.

(Other Example of the First Emitting Section)

The following are other examples of suitable luminescent materials ofthe first emitting section: Y₃(Al, Ga)₅O₁₂:Ce, (Ba, Ca, Sr)MgAl₁₀O₁₇:Eu,(Ba, Mg, Ca, Sr)₅(PO)₄Cl:Eu, (Ba, Ca, Sr)₃MgSi₂O₈:Eu, which have a peakwavelength between 400 nm and 500 nm; (Ba, Ca, Sr)MgAl₁₀O₁₇:Eu, Mn, (Ba,Ca, Sr)Al₂O₄:Eu, (Ba, Ca, Sr)Al₂O₄:Eu, Mn, (Ca, Sr)Al₂O₄:Eu,Eu-activated α-sialon represented by the general formulaCa_(x)Si_(12-(m+n))Al_((m+n))O_(n)N_(16-n): Eu(0.3<x<1.5, 0.6<m<3,0≦n<1.5), which have a peak wavelength between 500 nm and 600 nm. Itshould be noted that the above examples are by no means restrictive.

The above mentioned phosphors can be used either singly or ascombination of more than one phosphors in any possible combination andin any possible ratio.

Of the phosphors exemplified above, those having a garnet crystalstructure are preferred because they are resistant against heat, lightand water. As a concrete example of phosphors having a garnet crystalstructure can be cited a phosphor that has previously been cited as thefirst example of green light emitting phosphor and Y₃(Al, Ga)₅O₁₂:Ce.

(Examples of Substances Suitable as Luminescent Materials of the SecondEmitting Section)

(First Example of the Second Emitting Section)

As the first example of suitable luminescent materials of the secondemitting section can be cited the phosphors described by the formula (3)below.

M_(a)A_(b)D_(c)E_(d)X_(e)   Formula (3)

In the formula (3) above, M represents one or more than one elementsselected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy,Ho, Er, Tm and Yb. It contains Eu as a minimum requirement. A representsone or more than one elements selected from bivalent metal elementsother than M. D represents one or more than one elements selected fromtetravalent metal elements. E represents one or more than one elementsselected from trivalent metal elements. X represents one or more thanone elements selected from O, N, and F.

In the formula (3) above, a, b, c, d and e indicate a value in the rangeshown below.

0.00001≦a≦0.1

a+b=1

0.5≦c≦4

0.5≦d≦8

0.8×(2/3+4/3×c+d)≦e

e≦1.2×(2/3+4/3×c+d)

In the formula (3) above, M represents one or more than one elementsselected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy,Ho, Er, Tm and Yb. It contains Eu as a minimum requirement. Morepreferably, M represents one or more than one elements selected from thegroup consisting of Mn, Ce, Sm, Eu, Tb, Dy, Er, and Yb. Eu is theparticularly preferable element.

In the formula (3) above, A represents one or more than one elementsselected from bivalent metal elements other than M. Preferably, itrepresents one or more than one elements selected from Mg, Ca, Sr andBa. Particularly preferable is Ca or a mixed system consisting of Ca andSr.

Furthermore in the formula (3) above, D represents one or more than oneelements selected from tetravalent metal elements. Preferably, itrepresents one or more than one elements selected from the groupconsisting of Si, Ge, Sn, Ti, Zr and Hf. Si is the particularlypreferable element.

In the formula (3) above, E represents one or more than one elementsselected from trivalent metal elements. Preferably, it represents one ormore than one elements selected from the group consisting of B, Al, Ga,In, Sc, Y, La, Gd and Lu. Al is the particularly preferable element.

Furthermore in the formula (3) above, X represents one or more than oneelements selected from O, N, and F. Particularly preferred is N or acombination of N and O.

In the formula (3) above, a represents the content of M element whichplays the role of luminescent center. It is preferable to set a, theratio of the number of M atom to the number of (M+A) atom in thephosphor {a=(number of M atom/(number of M atom+number of A atom)), at0.00001 or larger, and 0.1 or smaller. If the value of a is smaller than0.00001, the number of M element constituting the luminescent center issmall and this may result in the lowering of emission brightness. If thevalue of a is larger than 0.1, concentration quenching due tointeraction among M ions themselves may occur, resulting in the loweringof emission brightness. In case the M element is Eu, it is preferablethat the value a is set in the range of 0.002 or larger, and 0.03 orsmaller, as it can have high emission brightness then.

Furthermore, in the formula (3) above, represents the content of Delement such as Si, and falls in the range of 0.5≦c≦4. Preferably, thevalue of c is in the range 0.5≦c≦1.8, more preferably c is 1. It islikely that emission brightness decreases in case the value of cissmaller than 0.5, and in case it is larger than 4. In the range0.5≦c≦1.8, emission brightness is high. It is particularly high in casethe value of c is 1.

Furthermore, in the formula (3) above, d represents the content of Eelement such as Al and falls in the range of 0.5≦d≦8. Preferably, thevalue of d is in the range 0.5≦d≦1.8, more preferably d is 1. It islikely that emission brightness decreases in case the value of d issmaller than 0.5, and in case it is larger than 8. In the range0.5≦d≦1.8, emission brightness is high. It is particularly high in casethe value of d is 1.

Furthermore, in the formula (3) above, e represents the content of Xelement such as N. The value of e is larger than or equal to0.8×{(2/3)+(4/3)×c+d}, and smaller than or equal to1.2×{(2/3)+(4/3)×c+d}. It is more preferable that e takes the value of3. In case the value deviates outside the above range, emissionbrightness is likely to decrease.

Of the compositions mentioned above, the preferable composition ensuringhigh emission brightness is such that it contains Eu as M element, Ca asA element, Si as D element, Al as E element, and N as X element as aminimum requirement. It is particularly preferable that it is aninorganic compound in which M element is Eu, A element is Ca, D elementis Si, E element is Al, and X element is N or a mixture of N and O.

This phosphor is excited by light whose wavelength is at least 580 nm orlower, the most efficient range being 400 nm to 550 nm. It, therefore,absorbs light coming from the first emitting section most efficiently.The emission spectrum has its peak in the range of 580 nm to 720 nm.

(Second Example of the Second Emitting Section)

As the second example of suitable luminescent materials of the secondemitting section can be cited the phosphors described by the formula (4)below.

Eu_(a)Ca_(b)Sr_(c)M_(d)S_(e)   Formula (4)

In the formula (4) above, M represents at least one element selectedfrom Ba, Mg, and Zn and a, b, c d and e indicate a value in the rangeshown below.

0.0002≦a0.02

0.3≦b≦0.9998

0≦d≦0.1

a+b+c+d=1

0.9≦e≦1.1

In terms of thermal stability, the preferable range of a in the formula(4) above is usually 0.0002 or larger, more preferably 0.0004 or larger,and usually 0.02 or smaller.

In terms of temperature characteristics, the preferable range of a inthe formula (4) above is usually 0.0004 or larger, and usually 0.01 orsmaller. Preferably, it is 0.007 or smaller, more preferably 0.005 orsmaller and still more preferably 0.004 or smaller.

From the viewpoint of emission intensity, the preferable range of a inthe formula (4) above is usually 0.0004 or larger. More preferably, itis 0.001 or larger. On the other hand, it should usually be 0.02 orsmaller. Preferably, it is 0.008 or smaller. If the content of Eu²⁺, theluminescent center ion, is smaller than that range described above,emission intensity tends to be lowered. On the other hand, if the valueof a is larger than that range described above, the phenomenon ofconcentration quenching occurs, this also causing the lowering ofemission intensity.

Taking into consideration all of thermal stability, temperaturecharacteristics and emission intensity, the preferable range of a in theformula (4) above is usually 0.0004 or larger, more preferably 0.001 orlarger, and usually 0.004 or smaller.

In the fundamental crystal structure Eu_(a)Ca_(b)Sr_(c)M_(a)S_(e) in theformula (4) above, the molar ratio of the cationic site, occupied by Eu,Ca, Sr or M, and anionic site, occupied by S, is 1:1. Cationicdeficiency or anionic deficiency, even if present to a small extent,does not seriously affect the fluorescence performance, required in thepresent invention. Therefore, the fundamental crystal of the aboveformula (4) maybe used, with the molar ratio e of the anionic siteoccupied by S above being in the range of 0.9 or larger and 1.1 orsmaller.

In the phosphor described in the formula (4) above, M, which representsat least one type of element selected from the group consisting of Ba,Mg, and Zn, is not necessarily an essential element in the presentinvention. However, even when it is contained in phosphor represented bythe formula (4) with a molar ratio d of M, which is 0≦d≦0.1, the objectof the present invention can be achieved.

The presence of elements other than Eu, Ca, Sr, Ba, Mg, Zn and S,contained as impurities in the phosphor shown in the formula (4) above,does not adversely affect its use if the content is 1% or less.

This phosphor is excited by light of the wavelength of 600 nm orshorter. The most efficient excitation is obtained at 400 nm to 550 nmand, therefore, it absorbs well the light emitted from the firstemitting section. The emission spectrum has its peak at 620 nm to 680nm.

[Other Examples of the Second Emitting Section]

Luminescent materials of the second emitting section can be any othersubstances emitting light of the wavelength of 550 nm to 750 nm, whichis longer than the light from the first emitting section. Examplesinclude the following: Eu-activated α-sialon represented by the generalformula

Ca_(x)Si_(12-(m+n))Al_((m+n))O_(n)N_(16-n):Eu (here, 0.3<x<1.5, 0.6<m<3,0≦n<1.5), Ca₂Si₅N₈:Eu, CaSi₇N₁₀:Eu, and Europium complex emittingfluorescence.

The above phosphors can be used either singly or as any combination ofmore than one substances in any possible combination and in any possibleratio.

[Diameter or the Like of Luminescent Materials]

Luminescent materials are usually used as particles. The diameter of theparticles of the luminescent materials is usually 150 μm or smaller.Preferably, the diameter is 50 μm or smaller, more preferably, 20 μm orsmaller, still more preferably 10 μm or smaller, most preferably 5 μm orsmaller. If the diameter is larger than the above range, the fluctuationof the luminescent color emerging from light emitting device tends to belarger. It is also likely that uniform application of luminescentmaterials becomes difficult in case luminescent materials are mixed witha sealing agent. The diameter is usually 0.001 μm or larger. Preferably,it is 0.01 μm or larger, more preferably, 0.1 μm or larger, still morepreferably 1 μm or larger, most preferably 2 μm or larger. Luminousefficiency is lowered below the above range.

The volume ratio of the luminescent materials of the second emittingsection to that of the first emitting section may take any value. Theratio is usually 0.05 or larger, preferably 0.1 or larger, morepreferably 0.2 or larger, and usually 1 or smaller, preferably 0.8 orsmaller, more preferably 0.5 or smaller. It is difficult to obtaindesirable white light when this ratio is too large or too small.

In case a binder is not used in preparing the first emitting section andthe second emitting section, luminescent materials can be calcinated,for example, and it is possible to use these sintered substancesdirectly for the first and the second emitting sections. Otherwise,luminescent materials can be made into glass, or single crystals ofthese substances can be manipulated, to prepare the first emittingsection and the second emitting section without using a binder. It isalso possible to add other additives and the like to the light emittingsections in the absence of a binder.

To the second emitting section are added luminescent materials, whichare excited by light from the light source and first emitting section,and emit light containing longer wavelength component than the firstemitting section, binder and other additional components. Furthermore,luminescent materials in the first emitting section can be added to thesecond emitting section. However, it is preferable to keep theconcentration of the luminescent materials of the first emitting sectioncontained in the second emitting section small in order to obtain alarger luminous flux. It is more preferable that the second emittingsection does not contain luminescent materials of the first emittingsection.

On the other hand, the first emitting section does not usually containluminescent materials of the second emitting section. However, it maycontain the luminescent materials of the second emitting section as longas luminous flux from the first emitting section does not decrease dueto such substances. It is preferable that the volume of such substancesin the first emitting section is less than or equal to 40 volume %. Itis more preferable that the luminescent materials of the second emittingsection are not contained at all. Luminescent materials of the secondemitting section can be excited by the light emitted from the firstemitting section. However, in the first emitting section, light emittedby the luminescent materials of the first emitting section should not beabsorbed excessively by the co-existing luminescent materials of thesecond emitting section. Luminescent materials of each section should beselected so that the above requirement is met.

I-2-2. Binder

As is mentioned above, the first and the second emitting sections maycontain binders in addition to luminescent materials. Binders areusually used to bind together luminescent materials present in thepowder form or in the particulate form, or to attach luminescentmaterials to a frame. There is no specific limitation on the binder ofthe present invention, and any known types of it may be usedarbitrarily.

However, in case light emitting devices are constructed to betransmissive type, which is composed in such a way that the lightemitted from the light source, the first emitting section and the secondemitting section passes through the first emitting section or the secondemitting section before leaving the light emitting device towardsoutside, it is preferable to select as binder such substances whichpermit transmission of every component of light emitted by the lightemitting device.

Resins and inorganic materials such as glass can be used as binder.Concrete examples include resins prepared by organic synthetic resinsuch as epoxy resins or silicone resins, and inorganic material such aspolysiloxane gel or glass.

When resin is used as binder, no particular limitation is imposed on itsviscosity. It is desirable to select a binder having suitable viscosity,taking into consideration the particle diameter and specific gravity,especially specific gravity per unit surface area, of luminescentmaterials used. For example, when epoxy resin is used as binder andparticle diameter of luminescent materials is in the range of 2 μm to 5μm with its specific gravity in the range of 2 to 5, it is desirable touse epoxy resin with viscosity of 1 Pas to 10 Pas. Under this condition,luminescent materials can be dispersed well.

It is to be noted that one kind of binder can be used singly, or two ormore kinds of binders can be used in any combination and in any ratio.

I-2-3. Ratio of Luminescent Material used

In case binder is added to the luminescent material, luminescentmaterials and binders can be mixed in any ratios. The weight ratio ofluminescent materials to binder is usually set to be larger than orequal to 0.01. Preferably, it is set to be larger than or equal to 0.05,and more preferably, it is set to be larger than or equal to 0.1. Theratio should usually be less than or equal to 5. Preferably, it is lessthan or equal to 1, and more preferably, it is less than or equal to0.5.

With a transmissive-type light emitting device, it is preferred that theluminescent materials are properly dispersed in the first emittingsection and the second emitting section in order to obtain largerluminous flux. On the other hand, with a light emitting device of lightreflection type (namely, light from light source, the first emittingsection and the second emitting section leaves the light emitting devicetowards outside without passing through the first and the secondemitting sections), it is preferred that luminescent materials arepacked in high density in order to obtain larger luminous flux. Theratio of the luminescent materials and binder should be decided, as wellas from the above-mentioned viewpoint, taking into consideration the useof light emitting device, kind and physicochemical property ofluminescent materials, and kind and viscosity of binders.

The color of light emitted from a light emitting device can be modifiedany way by adjusting the ratio of the luminescent materials of the firstemitting section and the second emitting section and by adjusting theamount of each luminescent material used. Thus, in addition to lightwith the chromaticity coordinate of (x=0.333, y=0.333), it is possibleto obtain intermediate-color light with the chromaticity coordinates of(x=0.47, y=0.42), (x=0.35, y=0.25), (x=0.25, y=0.30), and (x=0.30,y=0.40).

I-2-4. Other Components

Luminescent materials may contain additional components so that thefirst emitting section and second emitting section consist ofluminescent materials, appropriately used binders and other additionalcomponents.

Additional components are not limited to specific compounds and anyknown additives can be used. For example, in order to control lightdistribution characteristics or color mixing, diffusion agents such asalumina or yttria are preferred as additional components. Whenluminescent materials are packed in high density, adhesive agents suchas calcium pyrophosphate or barium calcium borate are preferable asadditional components.

I-2-5. Method of Production of Light Emitting Section

The method of production of the first and the second emitting sectionsare not limited to any specific method. These units can be produced inany way. Examples of the production method will be described below. Itshould be noted that methods other than those described here are alsopossible.

The first and the second emitting sections can be produced, for example,by first preparing slurry through dispersing luminescent materials,appropriately selected binder and additional components in a dispersionmedium, and by potting or coating the prepared slurry onto a basematerial such as a frame, followed by drying the slurry.

Slurry can be prepared by mixing into a dispersion medium luminescentmaterials, appropriately selected binder and additional components.Slurry may be termed paste or pellet depending on what is used asbinder. In this specification, the term slurry is used throughout.

The dispersion medium used for the preparation of slurry is not limitedto specific compounds, and thereby any known dispersion medium may beused. The examples include the following: chain hydrocarbons such asn-hexane, n-heptane or Solvesso, aromatic hydrocarbons such as tolueneor xylene, halogenated hydrocarbons such as trichloroethylene orperchloroethylene, alcohols such as methanol, ethanol, isopropanol orn-butanol, ketones such as acetone, methylethyl ketone or methylisobutylketone, esters such as ethyl acetate or n-butyl acetate, ethers such ascellosolve, butylsolve or cellosolve acetate, aqueous solvents such aswater or any aqueous solutions.

Then, slurry prepared is applied onto the base material such as a frame.There is no limitation on the method of application. Methods such asdispensing or potting can be used.

In case slurry is applied directly on the frame, the order ofapplication of slurry to be the first emitting section and the secondemitting section need not be fixed. Either section can be coated firstor the two sections can be coated simultaneously.

After application, dispersion medium is evaporated by drying to preparethe first emitting section and the second emitting section. There is nolimitation on the method of drying. Examples include natural drying,heated-air drying, vacuum drying, baking, UV curing, and electronirradiation. In particular, baking at several tens ° C. to one hundredand several tens ° C. is preferable because it requires only inexpensiveequipment with dispersion medium removed efficiently.

In case luminescent materials are packed in high density in order tomanufacture a light emitting device of light reflection type, asdescried earlier, it is preferable to add an adhesive agent to slurry asan additional component. Further, when slurry containing an adhesiveagent is applied, it is preferable to use such methods as screenprinting or ink jet printing, because it is then easy tocompartmentalize the first emitting section and the second emittingsection. Needles to say, usual methods of application can also be usedeven when an adhesive agent is used.

Further, the first emitting section and the second emitting section canbe prepared without using slurry. For example, luminescent materials andappropriately selected binder or other additives are mixed, kneaded andmolded into the first emitting section and the second emitting section.The method of molding includes: press molding, extrusion molding (T-dieextrusion, inflation extrusion, blow molding, melt spinning, contourextrusion and the like), and injection molding.

In case a binder is thermosetting like epoxy resin or silicone resin, itis possible to prepare the first emitting section and the secondemitting section by first mixing a binder, not yet cured, luminescentmaterials and appropriately selected other components, then by moldingand heating the mixture to cure the binder. In case a binder isUV-curable, it is possible to cure the binder resin by UV curing to makethe first emitting section and the second emitting section, instead ofheating in the above-mentioned process.

The first emitting section and the second emitting section can beprepared as one process of manufacturing the light emitting device.Otherwise, these units can be prepared as independent units first, andlater incorporated into the frame. Furthermore, it is also possible toprepare a unit combining the frame and either the first emitting sectionor the second emitting section. The light emitting device can becompleted by assembling these units.

In this connection, there is no limitation to the way in which a lightshielding unit is set up. For example, the first and the second emittingsections are made first, followed by setting a light shielding unitbetween them. Otherwise, a light shielding unit can be introduced in aframe first, and then the first and the second emitting sections areformed by applying the above-mentioned slurry and the like in the groovepartitioned by the light shielding unit.

I-3. Embodiments

In the following section are explained various embodiments in which thepresent invention is executed. The present invention is not restrictedto the following embodiments, but any modification is allowed within thescope of the present invention.

-3-1. First Embodiment

FIG. 1( a) and FIG. 1( b) show schematically the essential parts of alight emitting device as a first embodiment of the present invention.FIG. 1( a) is a cross-sectional view, and FIG. 1( b) is an explodedperspective view, with a divider plate removed for ease of explanation.

As shown in FIG. 1( a) and FIG. 1( b), the light emitting device 1 ofthe present embodiment consists of frame 2, blue LED (blue emittingsection) 3, which is a light source, green light emitting section 4,which functions as the first emitting section, red light emittingsection 5, which functions as the second emitting section, and dividerplate 6, which functions as light shielding unit.

Frame 2 constitutes a resinous base to hold blue LED 3, green lightemitting section 4, red light emitting section 5 and divider plate 6. Onthe upper side of the frame 2, a concave portion (a recession) 2Aopening upward in FIGS., whose cross-sectional view is trapezoidal, isformed. Therefore, the frame 2 is cup-like shaped and thus, enables thelight to be emitted from the light emitting device 1 in thepredetermined direction, leading to the effective use of emitted light.The dimension of the concave portion 2A of the light emitting device 1(such as the gradient of the slope or depth from the open end to thebottom) is arranged so that light can be emitted from the light emittingdevice 1 in the predetermined direction (upwards in the FIGS.).

At the bottom of the concave portion 2A, there is an electrode (notshown in the FIGS.) and electric power is supplied from outside thelight emitting device 1 to the blue LED 3 through that electrode.

The inner surface of the concave portion 2A of the frame 2 is metalplated and has a high reflectance through the entire region of visiblelight. Thereby, light irradiated on the inner surface of the concaveportion 2A of the frame 2 can emerge from the light emitting device 1 inthe predetermined direction. Needless to say, care must be taken so thatshort circuit does not occur between the metal plating and theelectrode.

At the bottom of the concave portion 2A of the frame 2 is installed ablue LED 3 as light source. Blue LED is a LED which emits blue light onelectric power supply. Part of the blue light emitted by blue LED 3 isabsorbed by luminescent material (in this case phosphor) in the greenlight emitting section 4 and red light emitting section 5 as excitinglight. Another part is designed to leave the light emitting device 1 inthe predetermined direction (here, upwards in the FIGS.).

As mentioned above, blue LED 3 is installed at the bottom of the concaveportion 2A of frame 2. Frame 2 and blue LED 3 are connected by means ofsilver paste (that is, a mixture of an adhesive agent and particles ofsilver) 7. Blue LED 3 rests on frame 2 by this mechanism. Furthermore,silver paste 7 plays a role in dissipating heat generated by blue LED 3.

Furthermore, frame 2 is fitted with a metal wire 8, which supplieselectric power to blue LED 3. Namely, the blue LED 3 and the electrode(not shown in the FIGS.) placed at the bottom of the concave portion 2Aof the frame 2 are connected by wire bonding using wire 8. By energizingthe wire 8, blue LED 3 is supplied with electric power, thereby emittingblue light.

In the concave portion 2A of the frame 2 are installed green lightemitting section 4 as the first emitting section and red light emittingsection 5 as the second emitting section.

The concave portion 2A is filled with green light emitting section 4 andred light emitting section 5. The surface of green light emittingsection 4 and red light emitting section 5 facing the outside of thelight emitting device 1 at the open end of the concave portion 2A isfunctioning as light exit side 1A of the light emitting device 1emitting light in the predetermined direction. In other words, from thislight exit side 1A is emitted, in the predetermined direction, bluelight emitted from the blue LED 3, green light emitted from the greenlight emitting section 4 and red light emitted from the red lightemitting section 5.

Green light emitting section 4 consists of green phosphor andtransparent resin. Green phosphor is a luminescent material of greenlight emitting section 4. It is a fluorescent material which is excitedby blue light emitted by blue LED 3, and emits green light which haslonger wavelength than blue light. Transparent resin functions as binderof green light emitting section 4. In this embodiment is used epoxyresin, a synthetic resin which permits transmission of visible lightthrough the whole range of wavelength.

Green light emitting section 4 is designed to fill the left side of theFIGS. from the bottom to the upper open end of the concave portion 2A.The green light emitting section 4 is also designed to cover the uppersurface and side surface other than the right side surface of the LED 3in the FIGS. Furthermore, the green light emitting section 4 occupies alarger space than the red light emitting section 5 in the concaveportion 2A.

Furthermore, the green light emitting section 4 has a first light exitside 4A at the open end of the concave portion 2A. This first light exitside 4A constitutes a flat-shaped upper surface of the green lightemitting section 4 in the FIGS., overlapping the flat-shaped surfaceconstituting the upper surface of frame 2. Furthermore, the first lightexit side 4A is a surface from which light emitted by green lightemitting section 4 is emitted to the outside of the light emittingdevice 1 in the predetermined direction. Also emitted from here is bluelight emitted by blue LED 3. Furthermore, the first light exit side 4A,in combination with the second light exit side 5A described later,constitutes a light exit side 1A of the light emitting device 1, fromwhich light emitted by the light emitting device 1 is emitted outwards.Therefore, green light emitting section 4 is open to the outside of thedevice through the light exit side 1A.

On the other hand, red light emitting section 5 consists of red phosphorand transparent resin. Red phosphor is a luminescent material of redlight emitting section 5. It is a luminescent material which is excitedby blue light emitted by blue LED 3 and green light emitted by greenlight emitting section 4, and emits red light which has longerwavelength than green light. Transparent resin functions as binder ofred light emitting section 5. In this embodiment, as is the case withgreen light emitting section 4, epoxy resin is used, which permitstransmission of visible light.

Red light emitting section 5 is designed to fill the right side of theFIGS. from the bottom to the upper open end of the concave portion 2A.As mentioned above, the green light emitting section 4 also extends fromthe bottom to the upper open end of the concave portion 2A. Therefore,the thickness of the green light emitting section 4 and that of the redlight emitting section 5 are designed to be approximately equal (asmeasured in the vertical direction in the FIGS). The red light emittingsection 5 is also designed to cover the right side surface of the blueLED 3 of the FIGS. Furthermore, the red light emitting section 5occupies a smaller space than the green light emitting section 4 in theconcave portion 2A.

Furthermore, the red light emitting section 5 has a second light exitside 5A at the open end of the concave portion 2A, analogously to greenlight emitting section 4. This second light exit side 5A constitutes aflat-shaped upper surface of the red light emitting section 5 in theFIGS., overlapping the flat-shaped surface constituting the uppersurface of frame 2. Furthermore, the second light exit side 5A is asurface from which light emitted by red light emitting section 5 isemitted to the outside of the light emitting device 1 in thepredetermined direction. Also emitted from here is blue light emitted byblue LED 3. As mentioned above, the second light exit side 5A, incombination with the first light exit side 4A, constitutes a light exitside 1A of the light emitting device 1, from which light emitted by thelight emitting device 1 is emitted outwards. Therefore, red lightemitting section 5 is open to the outside of the device through thelight exit side 1A.

Between green light emitting section 4 and red light emitting section 5,a divider plate 6 is installed as light shielding unit. It is fittedinto the insertion slit 2B made in the frame 2. The divider plate 6extends in depth direction from the open end of the concave portion 2Ato close to the blue LED. It is formed to be a rectangular, resinousplate covering the entire width of the concave portion 2A. The entiresurface of the divider plate 6 is metal plated like frame 2, therebyreflecting visible light efficiently.

Therefore, most of the light emitted by the green light emitting section4 is reflected by the divider plate 6 and does not enter the red lightemitting section 5. Similarly, most of the light emitted by the redlight emitting section 5 is reflected by the divider plate 6 and doesnot enter the green light emitting section 4. However, there is a verynarrow gap between the bottom of the concave portion 2A and the lowerend of the divider plate 6. At this gap, the green light emittingsection 4 and the red light emitting section 5 are in direct contactwith each other. Therefore, at this gap area, there can be traffic oflight between those two sections, although to a very limited extent.

The constitution of the light emitting device 1 of the presentembodiment is as described in the above sections. Therefore, when theblue light is emitted from the blue LED 3, a part of it is absorbed inthe green light emitting section 4 as exciting light and green light isemitted from the green light emitting section 4. Another part of theblue light emitted from the blue LED 3 is absorbed in the red lightemitting section 5 as exciting light and red light is emitted from thered light emitting section 5. A small quantity of light emitted from thegreen light emitting section 4 enters the red light emitting section 5through the gap, where the green light emitting section 4 and red lightemitting section 5 are in contact with each other, and is absorbed andused as exciting light there. In this process, each of blue light, greenlight and red light emitted is emitted from the light exit side 1A inthe predetermined direction.

Such a constitution of light emitting device 1 ensures high emissionefficiency and enhanced color rendering. Namely, the presence of thedivider plate 6 between the green light emitting section 4 and the redlight emitting section 5 works to prevent the light emitted from thegreen light emitting section 4 from entering the red light emittingsection 5. This reduces the quantity of the light emitted from the greenlight emitting section 4 absorbed in the red light emitting section 5,and leads to enhanced emission efficiency and color rendering. This samemechanism will also bring about reduction in fluctuation of the lightcomponents emitted from the light emitting device 1 and will help toimprove color reproduction property.

It is possible that green light emitted from the green light emittingsection 4 enters the red light emitting section 5 through the gap areapresent between the green light emitting section 4 and the red lightemitting section 5. However, that quantity is very small and does notadversely affect emission efficiency and color rendering. If green lightfrom the green light emitting section 4 is made never to enter the redlight emitting section 5 by separating the two sections using dividerplate 6 except at the portion where blue LED 3 and red light emittingsection 5 contact, emission efficiency and color rendering can be moresurely improved.

The surface of frame 2 and surface of divider plate 6 are designed toreflect all visible light efficiently. Blue light emitted by blue LED 3,green light emitted by green light emitting section 4 and red lightemitted by red light emitting section 5 are all emitted from light exitside 1A without being absorbed by frame 2 or divider plate 6. Thus, eachlight is utilized efficiently leading to high emission efficiency.

I-3-2. Second Embodiment

FIG. 2( a) and FIG. 2( b) show schematically the essential parts of alight emitting device as a second embodiment of the present invention.FIG. 2( a) is its cross-sectional view, and FIG. 2( b) is its explodedperspective view. For ease of explanation, in FIG. 2( a), the greenlight emitting section 14 and red light emitting section 15 areillustrated as much thicker sections than the actual ones. These twosections are in the thin film form to the extent that they are noteasily visible.

As shown in FIG. 2( a) and FIG. 2( b), the light emitting device 11 ofthe present embodiment consists of frame 12, blue LED (blue emittingsection) 13, which is a light source, green light emitting section 14,which functions as the first emitting section, red light emittingsection 15, which functions as the second emitting section, dividerplate 16 and beam 19.

Like frame 2 of the first embodiment, frame 12 constitutes a resinousbase to hold blue LED 13, green light emitting section 14, red lightemitting section 15, divider plate 16 and beam 19. On the upper side ofthe frame 12, a concave portion (a recession) 12A opening upward inFIGS., whose cross-sectional view is trapezoidal, is formed. Therefore,as is the case with the first embodiment, the light emitting device 11can emit light in the predetermined direction leading to enhancedemission efficiency.

The surface of the concave portion 12A of the frame 12 is metal platedand, therefore, light irradiated on this surface of the frame 12 can beemitted from the light emitting device 11 in the predetermined (upper,in the FIG.) direction.

On frame 12, beam 19 is placed from one end of the concave portion 12Ato the other end. This beam 19 is composed of material which enables atleast blue light emitted by blue LED 13, green light emitted by greenlight emitting section 14 and red light emitted by red light emittingsection 15 to pass through. The beam 19 is also fitted with an electrode(not shown in the FIG.) on its undersurface, which supplies electricpower to the blue LED 13.

Blue LED 13 is installed under the beam 19 as light source, in thecentral area. The blue LED 13 is similar to the one explained in thefirst embodiment and also functions similarly, and therefore, detailedexplanation is not given here. The blue LED 13 is fixed to the beam 19by means of silver paste 17 and is supplied with electric power throughwire 18 and the electrode. The silver paste 17 and wire 18 of thelight-emitting device 11 are similar to the silver paste 7 and wire inthe first embodiment.

On frame 12, green light emitting section 14 as the first emittingsection and red light emitting section 15 as the second emitting sectionare formed like a film with coequal thickness. The entire part of theinner surface of the concave portion 12A of the frame 12 is covered withfilms of green light emitting section and red light emitting section 15.

The light emitting device 11 is designed to emit light in thepredetermined, upper direction of the FIGS. The surfaces of the greenlight emitting section 14 and red light emitting section 15, which arenot in direct contact with frame 12 and divider plate 16, functions aslight exit side 11A, which permits emission of light from the lightemitting device 11 in the predetermined direction. Green light emittingsection 14 and red light emitting section 15 are opened to the outsidethrough this light exit side 11A. Consequently, from this light exitside 11A is emitted blue light from blue LED 13, green light from greenlight emitting section 14 and red light from red light emitting section15 in the predetermined direction. It is to be noted that blue lightfrom blue LED 13 is not emitted directly in the predetermined direction,but it is reflected by frame and then emitted to the outside of thedevice.

Furthermore, the space of the frame 12 extending from the bottom of theconcave portion 12A to the lower surface of the beam 19 is molded with amaterial (not shown in the FIG.) that permits transmission of blue lightfrom blue LED 13, green light from green light emitting section 14 andred light from red light emitting section 15.

Green light emitting section 14 is prepared by forming a film on thebottom and slope of the concave portion 12A of the frame 12, thematerial of which is similar to that of the green light emitting section4 described in the first embodiment. Furthermore, green light emittingsection 14 is prepared so that its film extends from the right end ofthe concave portion 12A to some point in the left half of the concaveportion 12A in the FIG. (here, in the left-hand side of the left end ofblue LED 13). Therefore, the green light emitting section 14 occupies alarger area than the red light emitting section 15.

On the other hand, red light emitting section 15 is prepared by forminga film on the surface of the concave portion 12A of the frame 12, thematerial of which is similar to that of the red light emitting section 5described in the first embodiment. Furthermore, red light emittingsection 15 is prepared on the bottom and slope of the concave portion12A where the green light emitting section 14 is not formed. As thegreen light emitting 14 extends from the right end and into the lefthalf of the frame 12 in the Fig., the red light emitting section 15 islocated away from the blue LED 13, in comparison with green lightemitting section 14.

Therefore, a larger quantity of the blue light from blue LED 13 entersthe green light emitting section 14, relative to the red light emittingsection 15.

In the light emitting device 11 as illustrated in this embodiment, adivider wall 16 is installed at the boundary of the green light emittingsection 14 and the red light emitting section 15. The divider wall 16extends in depth direction upwards from the bottom of the concaveportion 12A to close to the blue LED 13. The divider wall 16 isconnected to frame 12 as a rectangular, resinous plate covering theentire width of the concave portion 12A. The entire surface of thedivider wall 16 is metal plated like frame 12, thereby reflectingvisible light efficiently.

Therefore, most of the light emitted by the green light emitting section14 is irradiated on the divider wall 16 and does not enter the red lightemitting section 15. Similarly, most of the light emitted by the redlight emitting section 15 is irradiated on the divider wall 16 and doesnot enter the green light emitting section 14. However, there is a verynarrow gap between the divider wall 16 and the bottom of the concaveportion 12 and through this gap, there can be traffic of light betweenthe green light emitting section 14 and red light emitting section 15,although to a very limited extent.

The constitution of the light emitting device 11 is as described in theabove sections. Therefore, when the blue light is emitted from the blueLED 13, a part of it is absorbed in the green light emitting section asexciting light and green light is emitted from the green light emittingsection 14. Another part of the blue light emitted from the blue LED 13is absorbed in the red light emitting section 15 as exciting light andred light is emitted from the red light emitting section 15. A smallquantity of light emitted from the green light emitting section 14enters the red light emitting section 15 as exciting light through thegap at the upper end of the divider wall 16, and is absorbed and used asexciting light there. In this process, each of blue light, green lightand red light emitted is emitted from the light exit side 11A in thepredetermined direction.

Such a constitution of light emitting device 11 ensures high emissionefficiency and enhanced color rendering. Namely, the presence of thedivider wall 16 between the green light emitting section 14 and the redlight emitting section 15 works to prevent the light emitted from thegreen light emitting section 14 from entering the red light emittingsection 15. This reduces the quantity of the light emitted from thegreen light emitting section 14 absorbed in the red light emittingsection 15, and leads to enhanced emission efficiency and colorrendering. This same mechanism will also bring about reduction influctuation of the light components emitted from the light emittingdevice 11 and will help to improve color reproduction property.

It is possible that green light emitted from the green light emittingsection 14 enters the red light emitting section 15 through the gap atthe upper end of divider wall 16. However, that quantity is very smalland does not adversely affect emission efficiency and color rendering.If green light from the green light emitting section 14 is made never toenter the red light emitting section 15 by making the divider wall 16longer, emission efficiency and color rendering can be more surelyimproved.

The surface of frame 12 and surface of divider wall 16 are designed toreflect all visible light efficiently. Blue light emitted by blue LED13, green light emitted by green light emitting section 14 and red lightemitted by red light emitting section 15 are all emitted from light exitside 11A without being absorbed by frame 12 or divider wall 16. Thus,each light is utilized efficiently leading to high emission efficiency.

According to the light emitting device 11, the operations and effectssimilar to the light emitting device 1 of the first embodiment can bealso achieved.

I-4. Use of Light Emitting Device

There is no limitation to use of the light emitting device of thepresent invention, and it can be applied in any field where light isinvolved. As specific examples can be cited: lighting system, backlightunit for a display device, display device (or display), and so on.

There is no specific restriction when the light emitting device of thepresent invention is used as lighting system. It can be used in variousmodes as light emitting device, such as photoflash, lighting device forvideo camera, or indoor and outdoor lighting fixture. Pay attention tothat, in the light emitting device of the present invention, althoughwavelengths (or colors) of the lights emitted from the first and secondemitting section are different, light emerging from the light emittingdevice will spread sufficiently after leaving the light emitting deviceand will be perceived visually in a state where the lights from thelight source, first emitting section and second emitting section arewell mixed. Thereby, the lights can be observed to be intended color, byour visual perception, without being sorted into their wavelengthcomponents. By using light emitting device of the present invention aslighting system, light with high color rendering can be radiated, withhigh emission efficiency.

The light emitting device of the present invention can be also used asbacklight unit with optical elements like optical waveguide incombination. As an example can be cited a backlight unit installed at acellular phone display for illuminating liquid crystal display of thephone from backside. The light emitting device of the present inventioncan be used as this backlight unit for a display.

FIG. 3 is a schematical sectional view of the main part of a cellularphone display 21, for illustrating an example of a backlight unit usingthe light emitting device of the present invention. As shown in FIG. 3,on the backside of the liquid crystal display 22, an optical waveguide23, having the size corresponding to the entire backside of the liquidcrystal display 22, is installed. This optical waveguide 23 is aplate-like optical element, manufactured from the transparent materialthat can be passed through with the lights of all visible wavelengths,on the lateral side of which the light emitting device 24 is installed.This light emitting device 24 is installed in a manner that the lightemerging therefrom can enter the optical waveguide 23. And the backlightunit for a display 25 consists of this optical waveguide 23 and thelight emitting device 24. With this construction, the light emergingfrom the light emitting device 24 enters the optical waveguide 23, andthen emerges from a surface of the optical waveguide 23, facing theliquid crystal display 22, toward the liquid crystal display 22. Therebythe liquid crystal display 22 can be illuminated brightly. At thispoint, although the wavelengths (or colors) of the lights emitted fromthe first and second emitting sections of the light emitting device 24are different from each other, as the lights emerging from the lightemitting device 24 are mixed and homogenized within the opticalwaveguide 23, there is no possibility of irregularity in color onilluminating the liquid crystal display 22.

The light emitting device of the present invention is sometimes used asbacklight, which illuminates directly a liquid crystal display frombackside, for example when it is used for a relatively large type ofdisplay device (or display). Even in that case, there is no possibilityof irregularity in color, as the lights emerging from the light emittingdevice are mixed and homogenized on the way to the liquid crystaldisplay.

In this regard, some components like diffusion plate or light diffusionlayer can be used to spread light emerging from the light emittingdevice, for the purpose of mixing the wavelength components of the lightemerging from the light emitting device. With this construction, thelight can be more surely homogenized. This kind of method can bepreferably used for the use application that does not allow even a smallirregularity in luminescent color, for example indicators of audiovisualapparatuses.

As mentioned above, by using the light emitting device of the presentinvention as a backlight or backlight unit for a display device, it ispossible to propose a display with high color reproduction and highemission efficiency (or luminance).

II. Explanation about Display Device

In the following section is illustrated a third embodiment of thepresent invention, in which the display device of the present inventionis explained in detail. Though a third embodiment of the presentinvention is explained using Figs. below, the present invention is notrestricted to the following third embodiments, but any modification isallowed within the scope of the present invention.

FIG. 4 to FIG. 6 illustrate a third embodiment of the presentembodiment. FIG. 4 is a schematic, exploded perspective viewillustrating the summary of the display device. FIG. 5 is a schematicplane view of a backlight unit. FIG. 6 is a schematic cross-sectionalview of the essential part of the backlight unit.

The display device of the present embodiment comprises a backlight unit,image formation unit, and if necessary, other constituting members likediffusion plate, optical waveguide and so on.

FIG. 4 is a schematic, exploded perspective view illustrating a displaydevice of the present embodiment. As shown in FIG. 4, the display deviceof the present embodiment includes a backlight unit 101, diffusion plate102 and image formation unit 103.

II-1. Backlight Unit

Backlight unit 101 is a member emitting white light as backlight towardimage formation unit 103 via diffusion plate 102. The phrase of“backlight unit 101 emits white light” indicates not only such situationthat light turns to be white light just after it is emitted frombacklight unit 101 but also indicates broadly that light, not yet to bewhite light which is sufficiently dispersed just after it is emittedfrom backlight unit 101, is dispersed on the way to image formation unit103 and turns to be white light on arriving at image formation unit 103.

FIG. 5 is a schematic plane view of a backlight unit 101 used in thedisplay device of the present embodiment. As shown in FIG. 5, backlightunit 101 of the present embodiment has a plurality of (here, seven)light emitting sections 105 for emitting white light, on basal board 104which functions as frame. Each light emitting section 105 comprises agreen light emitting section 106 as the first emitting section and redlight emitting section 107 as the second emitting section.

II-1-1. Basal Board

Basal board 104 serves as a base to install light emitting section 105.It can be constituted similarly to the frame in the above-mentionedlight emitting device. Therefore, its shape and size are not limited tospecial ones and are to be determined depending on the shape, size oruse of the display device. For example, the light emitting section 105of the basal board 104 can take the shape of a board or cup. Its surfacecan be either flat, curved or concavo-convex. It is preferred to bedecided depending on its use.

There is no special limitation on the material of the basal board 104,either. Usually, it is preferable to use a material which does notpermit transmission of green light. Indeed, it is possible to use amaterial capable of transmitting green light. In that case, however, itis preferable to take some measure to block the green light, such ascoating the surface of the basal board 104 with a proper material thatcan prohibit transmission of at least green light. Blocking thetransmission of green light will be referred to in more detail later inthe explanation of the light emitting section 105.

As concrete example of materials for the basal board 104 can be citedthose used for the frame of the light emitting device, mentionedearlier. Particularly preferable is ceramics or the like among inorganicmaterials and glass epoxy resin or the like among organic materials. Itis possible to use one kind of material singly, or to use two or morekinds of materials in any combination and in any ratio.

Further, it is preferable to use for basal board 104 a material capableof liberating heat, for example, a material with high thermalconductivity. Usually, a light source in the light emitting section 105(See blue light source 108 in FIG. 6) releases heat during its use.Basal board 104 with a good heat liberation property assures its stableand continuous use even if heat is liberated during its use.

Furthermore, it is preferable to use, for a basal board 104, a materialwith good electrical insulation property.

In selecting a material for the basal board 104 in the constitution of adisplay device, it is desirable to pay attention to its color. The colormay be any color. However, usually, it is preferable to use a whitecolored or silver colored material. The reason is as follows. It ispossible that a part of white light emitted from the light emittingsection 105, and reflected by diffusion plate 102 or image formationunit 103, or light entering the display device from outside the device,is reflected by the surface of the backlight unit 101, located on theside where white light is emitted against the image formation unit 103(hereinafter referred to as “white light exit side”, as needed), andthat reflected light illuminates the image formation unit 103 from itsback. In that case, if the basal board 104 absorbs visible light,lowering of emission efficiency or color drift may occur. Therefore, itis preferable that the white light exit side of the basal board 104 iswhite or silver in color. Hence, it is preferable that the white lightexit side of basal board 104 is made of white- or silver-coloredmaterial.

It is preferable that a portion of the surface of the basal board 104,facing the green light emitting section 106 and the red light emittingsection 107 within the light emitting sections 105, has a highreflectance with regard to at least some components of the light, whichis reflected by the portion. It is more preferable that the reflectanceis heightened for all the wavelength region of visible light. Theemission efficiency of the backlight unit 101 can be further heightenedin this way. Therefore, it is preferable that at least an area of thebasal board reflected by light, as mentioned above, is made of materialhaving high reflectance. Examples of the methods of heighteningreflectance include those described above for the light emitting device.

Further, it is usual that the basal board 104 is fitted with electrodesand wiring to supply electric power. These electrodes and wiring can befitted any way. However, in constituting a display device, it isdesirable to use a through-hole on the back of the basal board 104 toprovide wiring pattern, because, then, the manufacturing of the basalboard is easy. There is no limitation on the material of the electrodesor wiring. Such materials as Cu, Au-plated Cu, Ag-plated Cu, Al and Agcan be used.

In the present embodiment, it is supposed that the basal board 104 ismade up in the shape of a white board and the surfaces facing the greenlight emitting section 106 and the red light emitting section 107 aretreated so that they can reflect all the wavelength of light in thevisible region. Also, it is supposed that the basal board 104 isequipped with an electrical wire 109 on its back, which supplieselectric power to the blue light source 108, and that at each positionthereof, corresponding to each light emitting section 105, it isequipped with an electrode 110 (See FIG. 6).

II-1-2. Blue Light Source

FIG. 6 is a schematic, cross-sectional view of light emitting section105. As is shown here in FIG. 6, light emitting section 105 comprisesgreen light emitting section 106 as the first emitting section and redlight emitting section 107 as the second emitting section. Green lightemitting section 106 and red light emitting section 107 are each fittedwith blue light source 108.

Blue light source 108 is alight source which emits blue light asexciting light to excite luminescent materials contained in green lightemitting section 106 and red light emitting section 107, similarly tothe light source described in the above light emitting device. It alsoemits blue light as one of the components of white light emitted bybacklight unit 101. In other words, a part of the blue light emitted byblue light source 108 is absorbed by luminescent materials in greenlight emitting section 106 and in red light emitting section 107 asexciting light, and another part of the blue light emitted is emitted sothat it is directed from backlight unit 101 towards image formation unit103.

There is no special limitation on the kind of blue light source 108 andappropriate one can be selected depending on the use and constitution ofdisplay device. It is preferred to select one which has equitableness inlight distribution and which diffuses light in wide directions.

As embodiment of blue light source 108, one similar to that describedfor the explanation of light emitting device can be cited. Usually,inexpensive LED is preferred.

When LED is used as blue light source 108, there is no speciallimitation on its shape. However, it is preferable to make its lateralside tapered in order to increase the external efficiency of lightproduction.

There is no special limitation on the kind of packaging material of LED,either. For example, ceramics or PPA (polyphthalamide) can beappropriately used. As is the case with basal board 104, preferablecolor for the package is white or silver from the standpoint ofimproving color reproduction. It is also preferable to achieve highreflectance of light from the standpoint of increasing emissionefficiency of backlight unit 101. When there is electrical wiring forblue light source 108, the same requirement as for the above-mentionedbasal board 104 and LED package can be applied for the color andreflectance of this wiring.

There is no special limitation on the method by which the blue colorlight source 108 is attached to the basal board 104. Soldering is onesuch method. The kind of solder is not limited to any special ones. Forexample, one similar to that described for the explanation of lightemitting device can be used. Especially when large-current-type LED orlaser diode, where heat dissipating property is important, is used asblue color light source 108, soldering is particularly useful because ofits excellent heat dissipating property.

In case a method other than soldering is to be used to attach the bluecolor light source 108 to the basal board 104, the methods explained forthe explanation of light emitting device can also be used. In this case,the use of a paste prepared by adding electroconductive filler such assilver particles or carbon particles to an adhesive agent, makespossible the electric power supply to the blue color light source 108via the adhesive agent, similarly to when soldering is used. The use ofelectroconductive filler is desirable also from the viewpoint ofincreasing heat dissipating property.

No particular limitation is imposed on the method of electric powersupply, either, to the blue color light source 108. Methods similar tothose described for the light emitting device can be applied.

The blue color light source 108 can be used as a single unit or as twoor more units together. Furthermore, only one kind of blue color lightsource 108 can be used or two or more different kinds of the lightsource 108 can be used.

Furthermore, one blue color light source 108 can be shared by greenlight emitting section 106 and red light emitting section 107, or thesame can be shared by more than one light emitting section 105. Usually,it is preferred to install the blue color light source 108 in each ofgreen light emitting section 106 and red light emitting section 107 inorder to enhance the color rendering of white light emitted by backlightunit 101.

There is no limitation on the wavelength of the blue light emitted bythe blue color light source 108, insofar as backlight unit 101 can emitlight of intended wavelength (in the present embodiment, white light).Usually, the wavelength is 350 nm or longer, preferably 370 nm orlonger, more preferably 380 nm or longer, still more preferably 400 nmor longer and most preferably 430 nm or longer. It is usually 600 nm orshorter, preferably 570 nm or shorter, more preferably 550 nm orshorter, still more preferably 500 nm or shorter and exceptionallypreferably 480 nm or shorter.

In particular, the wavelength of the blue light emitted by blue colorlight source 108, which is used for green light emitting section 106, isusually 350 nm or longer, preferably 400 nm or longer, more preferably430 nm or longer, and is usually 520 nm or shorter, preferably 500 nm orshorter, more preferably 480 nm or shorter.

On the other hand, the wavelength of the blue light emitted by bluecolor light source 108, which is used for red light emitting section107, is usually 400 nm or longer, preferably 450 nm or longer, morepreferably 500 nm or longer, and is usually 600 nm or shorter,preferably 570 nm or shorter, more preferably 550 nm or shorter.

In the present embodiment, LED emitting blue light is supposed to beused as blue color light source 108 in each of the green light emittingsection 106 and red light emitting section 107. The basal board 104 isfitted with conductive wire 109 on its back surface and electrode 110,which connects each blue color light source 108 and conductive wire 109,as shown in the FIG. 6. Electric power is supplied to the blue colorlight source 108 via conductive wire 109 and electrode 110.

II-1-3. Green Light Emitting Section and Red Light Emitting Section

Green light emitting section 106, which is the first emitting section,is designed to comprise at least one luminescent material (greenphosphor), which is excited by blue light emitted by blue color lightsource 108 and can emit green light containing light component in thegreen color region whose wavelength is longer than that of blue color.

Usually, green light emitting section 106 is prepared in such a way thatthe above-mentioned luminescent material is filled into a fillingportion (concave portion) formed in the basal board 104. Therefore, theshape of the green light emitting section 106 depends on the shape ofthe filling portion. There is no special limitation on the shape of thegreen light emitting section 106. Usually, a cup-shaped one, as shown inFIG. 6, is preferable, because this shape ensures that the light isemitted in the predetermined direction, which results in enhancedemission efficiency of backlight unit 101.

Green light emitting section 106 can be installed as a single unit inone location, or as two or more units in more than one location.Furthermore, the number of the green light emitting section 106installed can be set to be equal to or different from the number of redlight emitting section 107.

In the green light emitting section 106, luminescent materials emitlight on receiving blue light from blue color light source 108 asexciting light. Light thus emitted (green light) constitutes a componentof white light emitted outwards from the backlight unit 101 towards theimage formation unit 103.

On the other hand, red light emitting section 107, which is the secondemitting section, is designed to comprise at least one luminescentmaterial (red phosphor), which is excited by blue light emitted by bluecolor light source 108 and can emit red light containing light componentin the red color region whose wavelength is longer than that of bluecolor and above-mentioned green color.

Usually, red light emitting section 107 is prepared in such a way thatthe above-mentioned luminescent material is filled into a fillingportion (concave portion) formed in the basal board 104, similarly togreen light emitting section 106. Therefore, the shape of the red lightemitting section 107 depends on the shape of the filling portion. Thereis no special limitation on the shape of the red light emitting section107. Usually, it is preferable that the section is shaped like a cup,similarly to green light emitting section 106.

Red light emitting section 107 can also be installed as a single unit inone location, or as two or more units in more than one location.Furthermore, the number of the red light emitting section 107 installedcan be set to be equal to or different from the number of green lightemitting section 106.

In the red light emitting section 107, luminescent materials emit lighton receiving blue light from blue color light source 108 as excitinglight. Light thus emitted (red light) constitutes a component of whitelight emitted outwards from the backlight unit 101 towards the imageformation unit 103.

In this embodiment, however, the above-mentioned green light emittingsection 106 and red light emitting section 107, at least a part of themand preferably all of them, are designed to be formed as independentsections. By forming the green light emitting section 106 and red lightemitting section 107 separately from each other, the green light emittedfrom the green light emitting section 106, at least a part of it andpreferably all of it, is prevented from entering the red light emittingsection 107. Usually, it is better to prevent green light emitted fromthe green light emitting section 106 from entering the red lightemitting section 107 to such an extent that white light emitted from thebacklight unit 101 against the image formation unit 103 has sufficientlyhigh emission efficiency and color reproduction property to make itpractically usable. It is preferable that all the green light from thegreen light emitting section 106 is prevented from entering the redlight emitting section 107. Through this manipulation, it is possible toprevent the green light coming from the green light emitting section 106from being consumed as exciting light of the luminescent materials inthe red light emitting section 107, resulting in less decrease inemission intensity of the green light and increase in emissionefficiency of the backlight unit 101. Also, excessively high intensityof the red light from the red light emitting section 107 due toabsorption of the green light as exciting light is prevented, thisleading to the enhanced color rendering of white light emitted from thebacklight unit 101.

Usually, the green light emitting section 106 and the red light emittingsection 107 are formed by filling the respective luminescent materialinto the filling portion of the basal board 104. Green light from thegreen light emitting section 106 is usually blocked by the basal board104 and does not enter the red light emitting section 107. Namely, thepart of basal board 104 between the green light emitting section 106 andthe red light emitting section 107 functions as light shielding unit,described previously for the light emitting device. Needless to say, thematerial for the basal board 104 should be such that it blocks at leastgreen light, or the surface of the board should be so coated.

The above-mentioned blue light, green light and red light can beutilized most efficiently if the board is capable of not only preventingthe transmission of green light but also reflecting at least some,preferably all, of the blue, green and red light. This also increasesthe emission efficiency of the backlight unit 101.

There may be provided a wall to prevent the transmission of green light,between green light emitting section 106 and red light emitting section107, for the purpose of blocking the transmission of green light moresurely. The wall can be formed by, for example, making a portion of thewhite light exit side, on basal board 104, between green light emittingsection 106 and red light emitting section 107 to be convex. To use theconvex portion as wall can protect the transmission of green light moresurely. At this point, the shape, dimension or the like of this wall canbe decided arbitrarily. Material used to form the wall can also beselected arbitrarily and those similar to basal board 104 can beselected. It is preferred to heighten reflectance of the wall surface aswell, similarly to basal board 104. In this case, this wall alsofunctions as light shielding unit, mentioned above.

Furthermore, it is desirable that both green light emitting section 106and red light emitting section 107 are opened to the outside of thedevice at the white light exit side in order to prevent the green lightemitted by green light emitting section 106 from entering red lightemitting section 107, as mentioned above. In other words, it isdesirable that the green light emitted by green light emitting section106 is emitted from the white light exit side toward image formationunit 103 without passing through red light emitting section 107, andthat the red light emitted by red light emitting section 107 is emittedfrom the white light exit side toward image formation unit 103 withoutpassing through green light emitting section 106. Even in case there isa protective layer formed on the white light exit side, or there is acover placed on backlight unit 101, and the green or red light must passthrough some other members like this protective layer or cover beforeleaving backlight unit 101 for outside, green light emitting section 106and red light emitting section 107 are deemed opened if other memberlike the protective layer or cover is such that they allow the green andred light to pass through.

As described above, green light emitting section 106 and red lightemitting section 107, opened at the white light exit side, assures thatthe decrease in intensity of the green light and red light, which may beabsorbed in the other luminescent material or blocked by the othermembers, is kept small (or none at all). This can lead to the increasein emission efficiency of backlight unit 101, decrease in fluctuation ofwhite light components emitted from backlight unit 101, and improvementin color rendering. That the white light can be emitted surely usingthree primary colors, blue, red and green ensures excellent colorreproduction property, subject to proper selection of blue light source108, green light emitting section 106 and red light emitting section107.

Emission efficiency of above-described backlight unit 101 can beenhanced through basically the same mechanism as the light emittingdevice. Another detailed explanation on the mechanism of improving theemission efficiency of backlight unit 101 will be made below, incomparison with the conventional art and taking into account theparticular use for display device.

In the conventional art, where white light is generated without usingall of blue, green and red light at the same time, color reproductionproperty is not fully sufficient. Even in case all of blue, green andred light are used at the same time, a part of green light is absorbedand consumed by the luminescent material emitting red light, if whitelight is generated without separating light emitting section 105 intogreen light emitting section 106, containing green luminescent material,and red light emitting section 107, containing red luminescent material.As is the case with not only the instance such that green luminescentmaterial and red luminescent material are used mixed and diffused in thesame emitting section being, but also the instance where greenluminescent material and red luminescent material are used at separatedemitting sections, like in Patent Document 1. Therefore, the intensityof the green light, intended to emerge outside of backlight unit 101,gets lowered, leading to decrease in luminous flux of the white lightemerging from the backlight unit 101 and thus in emission efficiency. Inaddition, as the green light is consumed by the luminescent materialemitting the red light and thus red light is intensified excessively,optical component balance of the white light emerging from the backlightunit 101 is fluctuated, leading to decrease in color reproduction of thedisplay device.

Moreover, in the conventional construction, it is necessary to enlargethe ratio of the luminescent material in the green light emittingsection against the luminescent material which emits the red light toobtain a desired color of the white light emerging from the backlightunit 101, because of the compensation of light emitted from the greenlight emitting section and absorbed in the red light emitting section.However, color rendering of white light depends on kinds and usage ratioof luminescent material. That is why the color rendering of the lighthas been liable to get insufficient, because usage ratio of luminescentmaterial tends to drop out the optimal value very far in theconventionally constructed the backlight unit like Patent Document 1.

In contrast to this, in the backlight unit 101 used in the presentembodiment, green light can be prevented from entering red lightemitting section 107. This leads to the protection of decrease inintensity of green light and absorbed by the red light emitting section107. Consequently, emission efficiency of the backlight unit 101 can beenhanced compared to the conventional one.

In addition, as the red light emitting section 107 can be prevented fromabsorbing green light and emitting light, fluctuation in opticalcomponents of the white light from the backlight unit 101 can belowered. This leads to enhanced color rendering of the backlight unit101, resulting in also improved color rendering property and colorreproduction of the display device.

Green light emitting section 106 and red light emitting section 107 canbe disposed at any location insofar as light emitted from blue lightsource 108, green and red light emitting sections 106, 107 (or blue,green and red light) can be emitted from backlight unit 101. However, itis preferable to dispose them as light emitting section 105, formed byincorporating the green and red light emitting sections 106, 107 so thatthey can emit the intended white light, as shown in this embodiment. Itis desirable to pair green and red light emitting sections 106, 107 eachin possibly smallest number to constitute light emitting section 105 aslong as they can emit the intended colored white light, as the color ofwhite light depends on the color and the ratio of intensity of eachblue, green and red light. If it is necessary to increase the intensityof white light, it is preferred to increase the number of the lightemitting section 105, which is the number unit, from the standpoint ofease in designing and manufacturing. Though each light emitting section105 contains a single green and red light emitting section 106, 107respectively in this embodiment, each of them can be installed in two ormore as needed.

Green light emitting section 106 and red light emitting section 107 canalso be disposed at any location within light emitting section 105. Theycan be arranged side by side as in the present embodiment, or one can beinstalled surrounding the other. Any more complicated disposition can beselected.

When increasing the number of light emitting section 105, the lightemitting sections 105 can also be disposed at any location. However, thelight emitting sections 105 are preferred to be positioned at uniformintervals, because in that way the image formation unit 103 can beirradiated uniformly. Therefore, it is desirable that each lightemitting section 105 is disposed, as shown in FIG. 5, at each apex ofequilateral triangles (See dashed lines of FIG. 5), arrangedcontinuously altogether.

The size of green light emitting section 106 and red light emittingsection 107 can be selected arbitrarily. But usually it is designedsubject to the intended white light constitution. White light is emittedfrom backlight unit 101 toward image formation unit 103, as mixed lightconsisting of blue, green and red light. Accordingly, the perceivedcolor of the white light changes depending on the intensity of eachmixed light of blue, green and red. This fact requires the adjustment ofbalance in intensity of each blue, green and red light in order toobtain intended colored white light. One such method of adjusting thebalance in intensity of each blue, green and red light is to adjust thesize of green light emitting section 106 and red light emitting section107. Green light emitting section 106 is set to be larger compared tored light emitting section 107 in order to intensify green light, andgreen light emitting section 106 is set to be smaller compared to redlight emitting section 107 in order to weaken green light.

The method of adjusting the balance of each intensity of blue, green andred light is not restricted to the above-mentioned way of adjusting thesize of green light emitting section 106 and red light emitting section107, but any appropriate method can be used. For example, intended whitelight can be obtained also by adjusting the ratio of the value ofelectric power supplied on blue light source 108 installed at greenlight emitting section 106 to that of supplied on blue light source 108installed at red light emitting section 107. This method can also makean adjustment of the balance of each intensities of blue, green and redlight and generate intended white light.

Otherwise, when blue light source 108 is driven by electric pulses, theintended white color can be generated by adjusting the duty ratio of it.In other words, by adjusting the ratio of pulse lighting period of bluelight source 108 installed at green light emitting section 106 to thatof blue light source 108 installed at red light emitting section 107,the balance of each intensities of blue, green and red light can beadjusted and intended white light can be generated.

Further, by adjusting the ratio of amount of luminescent materialscontained in green light emitting section 106 to that in red lightemitting section 107, the balance of each intensities of blue, green andred light can be adjusted and intended white light can be generated.

For adjusting each color and the balance of each intensities of blue,green and red light, to obtain the intended white light, actually thelight emitted from green light emitting section 106 and red lightemitting section 107 will be used to make the adjustment. White lightgenerated by mixing blue, green and red light can be considered to be alight consisting of a mixed light of blue and green light (hereinaftercalled “short wavelength light”, as needed) and another mixed light ofblue and red light (hereinafter called “long wavelength light”, asneeded). On this aspect, short wavelength light is a light emitted fromgreen light emitting section, and long wavelength light is a lightemitted from red light emitting section. Accordingly, by controllinggreen light emitting section 106 and red light emitting section 107 toadjust the color and intensity of each short and long wavelength light,emitted from green and red light emitting section 106, 107 respectively,the intended color of white light, emitted from each light emittingsection 105, can be obtained.

At this point, the above-mentioned short wavelength light (or mixedlight consisting of blue light and green light) preferably takes achromaticity coordinate of (x, y), as shown in FIG. 7, in the rangesurrounded by (0.25, 0.65), (0.43, 0.52), (0.32, 0.33), and (0.18, 0.33)(shown by range I in FIG. 7). It is more preferably in the rangesurrounded by (0.27, 0.53), (0.34, 0.49), (0.27, 0.34), and (0.22, 0.35)(shown by range II in FIG. 7). It is because balance between theluminance and the color reproduction property is superior.

The chromaticity coordinate of the above-mentioned long wavelength light(or mixed light consisting of blue light and red light) can be decidedto be opposite to that of the short wavelength light based on thechromaticity coordinate of the intended white light.

In this embodiment, light emitting sections 105 are deemed to be formedby filling luminescent materials, corresponding to respective greenlight emitting section 106 and red light emitting section 107, andbinder into filling portions, arranged independently one by one on thebasal board 104 and having the same shapes (circular in upper surfaceand trapezoidal in cross-section). Each light emitting section 105 isdisposed, as shown in FIG. 6, at each apex of equilateral triangles,arranged continuously altogether (See dashed lines of FIG. 6), thisleading to the uniform intervals between each of the light emittingsections 105.

II-1-4. Composition of Light Emitting Section

The green light emitting section 106, which is the first emittingsection, contains luminescent materials capable of absorbing excitinglight and emitting green light. On the other hand, the red lightemitting section 107, which is the second emitting section, containsluminescent materials capable of absorbing exciting light and emittingred light. In these green and red light emitting sections 106, 107,luminescent materials are usually retained on the basal board 104 usinga binder.

II-1-4-1. Luminescent Material

Luminescent materials can be selected from any known such materials.Light emission can be through any mechanism including fluorescence orphosphorescence. In the green light emitting section 106 as well as inthe red light emitting section 107, luminescent materials can be eithera single sort of substance or a mixture of more than one sorts ofsubstance in any possible combination or in any possible ratio. However,it is desirable that the luminescent materials in each of the greenlight emitting section 106 and red light emitting section 107 areappropriately selected, taking into consideration the chromaticitycoordinate of the intended white light.

There is no special limitation on the wavelength of the green lightemitted by the green luminescent material used in the green lightemitting section 106, so long as the backlight unit 101 can emit whitelight. Preferably, it is in the same range of wavelength as thatconsidered desirable for the luminescent material of the first emittingsection described in the above-mentioned light emitting device.

On the other hand, there is no special limitation either on thewavelength of the red light emitted by the red luminescent material usedin the red light emitting section 107, so long as the backlight unit 101can emit white light. Preferably, it is in the same range of wavelengthas that considered desirable for the luminescent material of the secondemitting section described in the above-mentioned light emitting device.

It is preferable to use luminescent materials having luminous efficiencyof 40% or higher, preferably 45% or higher, more preferably 50% orhigher, still more preferably 55% or higher, most preferably 60% orhigher. The luminous efficiency mentioned here represents a product ofquantum absorbing efficiency and internal quantum efficiency.

Luminescent materials referred to as desirable for the first emittingsection of the above-mentioned light emitting device can also be citedas desirable luminescent materials of the green light emitting section106. Likewise, luminescent materials referred to as desirable for thesecond emitting section of the above-mentioned light emitting device canalso be cited as desirable luminescent materials of the red lightemitting section 107.

When used for the constitution of a display device as well, luminescentmaterials, both for green light emitting and for red light emitting, areusually used as particles. The diameter of the particles can be anyappropriate one, but usually 150 μm or smaller. Preferably, the diameteris 50 μm or smaller, more preferably, 20 μm or smaller, still morepreferably 15 μm or smaller. If the diameter is larger than the aboverange, the fluctuation of the white color emerging from the backlightunit 101 tends to be larger. It is also likely that uniform applicationof luminescent materials becomes difficult in case luminescent materialsare mixed with a sealing agent (binder). The diameter is usually 0.001μm or larger. Preferably, it is 0.01 μm or larger, more preferably, 0.1μm or larger, still more preferably 1 μm or larger, still morepreferably 2 μm or larger, most preferably 5 μm or larger. Luminousefficiency is lowered below the above range.

In case green light emitting section 106 and red light emitting section107 are prepared without using a binder, for example, these sections canbe prepared in the same way as the first emitting section and the secondemitting section mentioned above for light emitting device.

Further, to the red light emitting section 107 are added luminescentmaterials capable of emitting red light, binder and other additionalcomponents.

Furthermore, luminescent materials emitting green light can also beadded. However, it is preferable to keep the concentration of the greenluminescent materials contained in the red light emitting section 107small in order to obtain a larger luminous flux. It is preferable thatthe red light emitting section 107 does not contain green luminescentmaterials.

On the other hand, the green light emitting section 106 does not usuallycontain luminescent materials emitting red light. However, it maycontain red luminescent materials as long as luminous flux of the greenlight does not decrease due to such materials. It is preferable that thevolume of red luminescent materials in the green light emitting section106 is less than or equal to 40 volume %. It is more preferable that redluminescent materials are not contained in the green light emittingsection 106 at all.

Red luminescent materials can be excited by green light. However, in thegreen light emitting section 106, the green light emitted by the greenluminescent material should not be absorbed excessively by theco-existing red luminescent material. Luminescent materials in each ofthe green and red light emitting section 106, 107 should be adjusted sothat the above requirement is met.

II-1-4-2. Binder

As is mentioned above, the green light emitting section 106 and the redlight emitting section 107 may contain binders in addition toluminescent materials. As is the case with the above-mentioned lightemitting device, binders are usually used to bind together luminescentmaterials present in the powder form or in the particulate form, or toattach luminescent materials to the basal board 104. Any known binderscan be used for the backlight unit 101.

However, in case backlight unit 101 is constructed to be transmissivetype, which is in such a way that the light emitted from the blue lightsource 108, the green light emitting section 106 and the red lightemitting section 107 passes through the green light emitting section 106or the red light emitting section 107 before leaving the backlight unit101 towards outside, as shown in FIG. 6, it is preferable to select asbinder such substances which permit transmission of each component ofwhite light (namely, blue light, green light and red light) emitted bybacklight unit 101.

As an example of a binder, one similar to that of the above-mentionedlight emitting device can be cited.

When resin is used as binder, no particular limitation is imposed on itsviscosity. It is desirable to select a binder having suitable viscosity,taking into consideration the particle diameter and specific gravity,especially specific gravity per unit surface area, of luminescentmaterials used. For example, similarly to the above-mentioned lightemitting device, when epoxy resin is used as binder and particlediameter of luminescent materials is in the range of 2 μm to 5 μm withits specific gravity in the range of 2 to 5, it is desirable to useepoxy resin with viscosity of 1 Pas to 10 Pas. Under this condition,luminescent materials can be dispersed well.

It is to be noted that one kind of binder can be used singly, or two ormore kinds of binders can be used in any combination in any ratio.

II-1-4-3. Ratio of Luminescent Material Used

In case binder is added to the green light emitting section 106 or tothe red light emitting section 107, luminescent materials and binderscan be mixed in any ratios. The weight ratio of luminescent materials tobinder is usually set to be 0.01 or larger. Preferably, it is set to be0.05 or larger, and more preferably, it is set to be 0.1 or larger. Theratio should usually be 5 or smaller. Preferably, it is 1 or smaller,and more preferably, it is 0.5 or smaller.

With a transmissive type backlight unit 101, it is preferred that theluminescent materials are properly dispersed in the green light emittingsection 106 and the red light emitting section 107 in order to obtainlarger luminous flux. On the other hand, with a backlight unit 101 oflight reflection type (namely, light from blue light source 108, thegreen light emitting section 106 and the red light emitting section 107leaves the light emitting device towards outside without passing throughthe green and the red light emitting sections 106, 107. See FIG. 8), itis preferred that luminescent materials are packed in high density inorder to obtain larger luminous flux. Therefore, taking these thingsinto consideration, the composition of luminescent materials should bedecided depending on the use of display device, kind and physicochemicalproperty of luminescent materials, and kind and viscosity of binders.

The color of white light emitted from the backlight unit 101, inaddition to generating usual white light with a chromaticity coordinateof (x, y)=(0.33, 0.33), can be modified any way in order to correct thetransmission characteristics of an image formation unit comprising anycombination of a liquid crystal plate, display plate, diffusion plate,optical waveguide and the like. It is possible to generate light havinga chromaticity coordinate in the range surrounded by (0.28, 0.25),(0.25, 0.28), (0.34, 0.40), and (0.40, 0.34).

II-1-4-4. Other Components

Luminescent materials may contain additional components so that thegreen light emitting section 106 and the red light emitting section 107consist of luminescent materials, appropriately used binders and otheradditional components.

Additional components are not limited to specific compounds and anyknown additives can be used. For example, additives similar to the onedescribed for the above-mentioned light emitting device can be used.

II-1-4-5. Method of Preparing Light Emitting Section

The method of preparing the green light emitting section 106 and the redlight emitting section 107 is not limited to any specific method. Forexample, these units can be prepared in a method similar to the onedescribed for the first emitting section and the second emitting sectionof the above-mentioned light emitting device.

In this embodiment, it is assumed that the green light emitting section106 and the red light emitting section 107 are each composed ofappropriate phosphors and binders. The amount and kind of luminescentmaterials and the size of the green and red light emitting section 106,107 are assumed to be set so that the light emitted from the backlightunit 101 can be white light {namely, light with a chromaticitycoordinate of (x=0.33, y=0.33)} when dispersed with the diffusion plate102, if appropriate blue light is emitted from the blue light source108.

II-2. Diffusion Plate

A diffusion plate 102 is a member for dispersing the light emitted frombacklight unit 101. This diffusion plate 102 is installed betweenbacklight unit 101 and image formation unit 103, as shown in FIG. 4. Thelight emitted from backlight unit 101 is dispersed within the diffusionplate 102 and comes to be white light, which then emitted toward imageformation unit 103.

There is no limitation on concrete constitution of diffusion plate 102.Therefore, any shape, material, size or the like thereof can beselected, resulting in that any known diffusion plate can be used.Examples include: a sheet with convexoconcave on both sides; and astructure formed so that minute particles of synthetic resin, glass orthe like is dissipated in a binder such as synthetic resin. In thelatter instance, light diffusion is achieved through the mechanismcaused by the difference in refractive index between the binder andminute particles. The sheet, binder, minute particles or the like usedin these examples are usually formed from materials which allow eachcomponent of white light emitted from backlight unit 101, which is blue,green and red light, to pass through.

In this embodiment, it is assumed that a sheet having convexoconcave onboth sides and transparent for visible light is used as diffusion plate102.

II-3. Image Formation Unit

An image formation unit 103 forms images at the front side thereof whenirradiated with above-mentioned white light emitted by backlight unit101 on the back side thereof. There is no specific limitation on it andany known one having any shape, size, material and so on can be used,insofar as it can form some images and allow the transmission of atleast a part of backlight radiated thereon.

As examples of image formation unit 103 can be cited a liquid crystalunit used in liquid crystal displays or the like, and a indicator usedin internal lighting indicators.

One example of a liquid crystal unit is such that a liquid crystallayer, formed by color filter, transparent electrode, oriented film,liquid crystal, another oriented film and another transparent electrodein this order, is retained within a case like glass cell with polarizingfilm on front side and back side. In this example of liquid crystalunit, images are formed by controlling the molecular arrangement ofliquid crystal using an electrode for energizing the transparentelectrodes. At that time, with the white light (backlight) radiated fromthe above-mentioned backlight unit 101 onto this liquid crystal unitfrom back side, the images formed at the liquid crystal unit can beclearly displayed at the front side of the liquid crystal unit.

Images formed on image formation unit can be displayed at any positionby the display device, insofar as it is at the front side of the imageformation unit. The images can be displayed at the front side of theimage formation unit directly, as well as they can be displayed byprojecting the image on some projection screen. This kind of example isa liquid crystal projector.

In case an indicator is used as image formation unit, images formed onthe indicator can be clearly displayed at the front side of theindicator by illuminating the indicator from back side with white light(backlight) emitted from the above-mentioned backlight unit 101.

Any type of images, such as letters or graphics, can be formed at theimage formation unit 103.

In this embodiment, a liquid crystal unit that displays images directlyat the front side thereof is used as image formation unit 103.

II-4. Advantageous Effects

When the display device of the present embodiment, havingabove-mentioned constitution, is used, it should be applied withappropriate electric power through wiring 109 and electrode 110, inorder to allow blue light source 108 of backlight unit 101 to emitintended white light. The blue light source 8, applied with electricpower, emits blue light with intensity corresponding to the electricpower supplied. A part of the blue light is directed to the diffusionplate 102 as one component of white light, and another part of it isabsorbed by the luminescent materials within the corresponding greenlight emitting sections 106 and red light emitting sections 107.

Green light emitting section 106 emits green light on excitation of bluelight absorbed by the luminescent material. This green light is directedto the diffusion plate 102 as one component of white light. On the otherhand, red light emitting section 107 emits red light on excitation ofred light absorbed by the luminescent material. This red light is alsodirected to the diffusion plate 102 as one component of white light. Atthis point, as green and red light emitting section 106, 107 are formedindependently from each other, green light is not absorbed by theluminescent material of red light emitting section 107. This enables theprevention of lowering the luminous flux of green light and ofdisturbing the balance of components included in white light.

Blue, green and red light emitted from backlight unit 101 entersdiffusion plate 102 and is dissipated within the diffusion plate 102.And then it is emitted toward image formation unit 103. The lightemitted from backlight unit 101 may be perceived visually as the lighthaving irregularly divided colors, because it is not yet dissipatedsufficiently before entering diffusion plate 102. However it isdissipated within the diffusion plate 102 and can be excellent whitecolored light, perceived visually as white light, at the moment ofreaching image formation unit 103.

Image formation unit 103 is irradiated with white light emitted fromdiffusion plate 102 from back side, which makes images formed on imageformation unit 103 be displayed clearly at the front of image formationunit 103. The color reproduction property, with this images displayed onimage formation unit 103, can be highly improved, because the whitelight contains blue, green and red light components and the balance ofthe components of the white light can be maintained well.

Further, decrease in the luminous flux can be prevented, as green lightis not allowed to be absorbed by the luminescent material within redlight emitting section 107. This results in the saving of the energy toproduce backlight. In other words, emission efficiency of backlight canbe enhanced.

II-5. Others

Although the third embodiment of the present invention has beenexplained in detail, it is to be understood that the display device ofthe present invention is not limited to the third embodiment and it canbe modified anyway insofar as it does not depart from the scope of theinvention.

For example, either green light emitting section 106 or red lightemitting section 107 may be formed as reflecting type of one, as shownin FIG. 8. Namely, in the constitution of FIG. 8, blue light source 108is installed apart from basal board 104 by beam 111, and green and redlight emitting sections 106, 107 are formed by coating them on thesurface of concave portion of basal board 104. Wiring 109 and electrodes108 are positioned at the surface of basal board 104 and beam 111respectively, so as to allow electric power to be supplied to blue lightsource 108. Other than these, green light emitting section 106 and redlight emitting section 107 of FIG. 8 is constructed in similar way tothe above-mentioned third embodiment. In this instance, a part of bluelight emitted from blue light source 108 is emitted to image formationunit 103 as one component of white light and another part of it isdirected to green light emitting section 106 and red light emittingsection 107. At green light emitting section 106 and red light emittingsection 107, formed on the surface of concave portions, the luminescentmaterial is excited by the blue light and emit green light and redlight. After all, backlight unit 101 can emit white light. In addition,as green light emitting section 106 and red light emitting section 107are installed independently from each other, green light is not absorbedby the luminescent material of red light emitting section 107 when it isemitted. This enables the prevention of lowering the luminous flux ofgreen light and of fluctuating the balance of components included inwhite light. In FIG. 8, the components having the same reference lettersas in FIGS. 4 to 7 show the same components as in FIGS. 4 to 7.

Further, green light emitting section 106 and red light emitting section107 may be formed by using a surface mount type frame. A backlight unit101 with this surface mount type frame is sometimes preferred dependingon the use of the display device.

One concrete example of the constitution of light emitting section 105using surface mount type frame is illustrated in FIG. 9. FIG. 9 is aschematic, cross-sectional view of one example of the constitution of alight emitting section 105 using a surface-mounted type frame. In FIG.9, the components having the same reference letters as in FIGS. 4 to 8show the same components as in FIGS. 4 to 8.

In the constitution of FIG. 9, a green light emitting section 106 and ared light emitting section 107, formed within a different frame 112respectively, are installed on one side of basal board 104. This pair ofgreen and red light emitting section 106, 107 forms a light emittingsection 105.

It is desirable to form frame 112 so that shape, size, material(including heat dissipating property, color and reflection) and the likethereof are similar to those of basal board 104 described particularlyin the above-mentioned third embodiment, as well as that it is notallowed to pass through any green light emitted from green lightemitting section 106. In FIG. 9, it is assumed that each light emittingsection 105 has a pair of frame 112, each of which is cup-shaped, withconcave portion, and that it has wiring 113 formed to connect betweenthe bottom of the concave portion and the underside of frame 112. It isalso assumed that a blue light source 108, having a wiring 113connected, is installed in each of the above-mentioned frame 112, whichis paired two by two, and that one frame 112 of the pair is filled withgreen luminescent material and binder to form green light emittingsection 106 and the other frame 112 of the pair is filled with redluminescent material and binder to form red light emitting section 107.Basal board 104 is supposed to be formed with through-holes 114, each ofthem having an electrode 110 installed. The electrodes 110 can besupplied with electric power via wirings 109 formed on the backside ofbasal board 104. The electrodes 110 and wirings 113 of frames 112 areconnected using solder 115, which makes it possible to apply electricpower to blue light source 108. The solder 115 is assumed to havefunctions not only of applying electric power to blue light source 108but also of fixing green and red light emitting sections 106, 107 ontobasal board 104, as well as of releasing heat generated at green and redlight emitting sections 106, 107.

In this instance, where light emitting section 105 is constituted usinga surface-mounted type frame, a part of blue light emitted from bluelight source 108 is emitted to image formation unit 103 as one componentof white light and another part of it is directed to green lightemitting section 106 and red light emitting section 107. Green lightemitting section 106 and red light emitting section 107, formed on thesurface of concave portions, are excited by the blue light and emitgreen light and red light. After all, backlight unit 101 can emit whitelight. In addition, as green light emitting section 106 and red lightemitting section 107 are installed independently from each other, greenlight is not absorbed by the luminescent material of red light emittingsection 107 when it is emitted. This enables the prevention of loweringthe luminous flux of green light and of fluctuating the balance ofcomponents included in white light.

An optical waveguide may be used for leading the white light frombacklight unit 101 to image formation unit 103, for another example.With this optical waveguide, backlight unit 101 can be disposed at thelocation other than the facing position to image formation unit 103 asin the above-mentioned embodiment. This results in the heightenedpossibility of display device design. There is no specific limitation onthe optical waveguide. Any known ones, such as mirror, prism, lens oroptical fiber, can be used arbitrarily.

FIG. 10 is a schematic cross-sectional view illustrating theconstitution of a display device using an optical waveguide. By using anoptical waveguide, backlight unit 101 can be positioned at a lateralside of image formation unit 103, as exemplified in FIG. 10. In theconstitution of FIG. 10, an optical waveguide 117 having reflection film116 on the back side is used. Here, white light introduced from alateral side (right hand side of Fig.) is reflected at reflection film116 and then guided toward diffusion plate 102, located at the front(upper side of Fig.). With this construction as shown in FIG. 10,backlight unit 101 can be positioned at a lateral side of imageformation unit 103. In FIG. 10, the components having the same referenceletters as in FIGS. 4 to 9 show the same components as in FIGS. 4 to 9.

For another example, the display device may comprise some othercomponents, such as antiflection film, view expansion film,luminance-enhancing film, lens sheet, protective cover, heat dissipationplate or the like, as needed.

It is possible to incorporate the constitutions described in theexplanation about light emitting device and those described in theexplanation about display device. It is also possible to combine each ofabove-mentioned embodiments and modifications.

The constitution of third embodiment can be achieved using light sourcesor luminescent materials emitting lights other than blue, red and green.

Light emitting devicees or backlight units may comprise three or morelight emitting sections, by providing a third emitting section to theabove-mentioned light emitting device or by providing a yellow lightemitting section to the backlight unit.

Examples

The present invention will be explained in further detail belowreferring to examples. It is to be understood that the present inventionis not limited to specific examples explained below and it can bemodified anyway insofar as it does not depart from the scope of theinvention.

Example 1

(Preparation of Green Light Emitting Section)

The green light emitting section was prepared so that the mixed light(short wavelength light) consisting of blue light and green light,emitted from the green light emitting section, gives a chromaticitycoordinate of (x, y)=(0.25, 0.35). The detail was as follows.

By using a surface mount type frame, as shown in FIG. 9, having aconcave portion of about 2.5 mm in diameter and about 0.9 mm in depth, ablue LED (C460MB, made by Cree) was placed on the bottom of the concaveportion of the frame as blue light source so that electric power issupplied to the blue light source from behind the board. In that concaveportion fitted with the blue light source, paste consisting of aluminescent material Ca_(2.94) Ce_(0.06) Sc_(1.94) Mg_(0.06) Si₃O₁₂ andsilicone resin (binder) was filled to form a green light emittingsection. The ratio of the luminescent material and the binder wasapprox. 95:5 by weight.

(Preparation of Red Light Emitting Section)

The red light emitting section was prepared so that the mixed light(long wavelength light) consisting of blue light and red light, emittedfrom the red light emitting section, gives a chromaticity coordinate of(x, y)=(0.56, 0.27). More specifically, as luminescent material,Ca_(0.992) AlSiEu_(0.008)N_(2.85)O_(0.15) was used. The ratio of theluminescent material and the binder was set at approx. 98:2 by weight.Other details were similar to those described for the green lightemitting section.

(Measurement of White Light)

Electric current of 20 mA was supplied to the blue LED of both the greenlight emitting section and the red light emitting section, and the LEDwas allowed to emit light. Light emitted from each of green and redlight emitting section was measured for the emission spectrum of theemitted light, using a spectroscope HR2000 (Ocean Optics) and anintegrating sphere for LED (Ocean Optics). It was confirmed that thechromaticity coordinate of the emitted light coincides with the intendedchromaticity coordinate.

Based on the result of the measurement, white light giving achromaticity coordinate of (x, y)=(0.33, 0.33) was generated from thelight emitted from the green and red light emitting sections, and theemission spectrum, of the white light, was calculated. Namely, as shownin FIG. 11, an attempt was made to generate white light having achromaticity coordinate on the line segment connecting the chromaticitycoordinate of light (short wavelength light) from the green lightemitting section and that of light (long wavelength light) from the redlight emitting section. Emission intensity of light from both of greenand red light emitting sections was calculated and adjusted to realizethe intended white light. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.48:0.52. Calculated emission spectrum isshown in FIG. 12. FIG. 11 is a chromaticity diagram illustrating themethod of generating white light in Example 1 to 4. Plots at both endsof each line segment represent chromaticity coordinates of the lightfrom the green light emitting section and the red light emitting sectionrespectively.

The entire luminous flux from the white light was 1.2 lm per one blueLED.

Example 2

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.27, 0.39).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.45, 0.22).

White light was generated similarly to Example 1 except that thechromaticity coordinate of the white light was set to (x, y)=(0.32,0.33), and the emission spectrum was calculated. In this example,spectral ratio of the light from the green light emitting section andthat from the red light emitting section was set at 0.50:0.50. FIG. 13shows the emission spectrum, as calculated in this example.

The entire luminous flux from the white light was 1.3 lm per one blueLED.

Example 3

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.28, 0.42).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.42, 0.21).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.47:0.53. FIG. 14 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.3 lm per one blueLED.

Example 4

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.30, 0.47).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.38, 0.18).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.46:0.54. FIG. 15 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.3 lm per one blueLED.

Example 5

The green light emitting section was prepared in the same method asdescribed for Example 1, except that Ca_(2.94)Ce_(0.06)Sc₂Si₃O₁₂ wasused as green luminescent material and the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(short wavelength light) consisting of blue light and green light givesa chromaticity coordinate of (x, y)=(0.24, 0.37).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.52, 0.26).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.52:0.48. Further, a chromaticity diagramillustrating the method of generating white light in Example 5 to 7 isshown in FIG. 16. In this FIG. 16, as in FIG. 11, plots at both ends ofeach line segment represent chromaticity coordinates of light from thegreen light emitting section and the red light emitting section in eachexample. FIG. 17 shows the emission spectrum, as calculated in thisexample.

The entire luminous flux from the white light was 1.0 lm per one blueLED.

Example 6

The green light emitting section was prepared in the same method asdescribed for Example 5, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.25, 0.40).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.45, 0.22).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.54:0.46. FIG. 18 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.0 lm per one blueLED.

Example 7

The green light emitting section was prepared in the same method asdescribed for Example 5, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.26, 0.42).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.42, 0.21).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.54:0.46. FIG. 19 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.0 lm per one blueLED.

Example 8

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.25, 0.35).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except thatCa_(0.1984)Sr_(0.7936)Eu_(0.008)AlSiN₃ was used as the luminescentmaterial of red light emitting section and the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.51, 0.29).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.48:0.52. Further, a chromaticity diagramillustrating the method of generating white light in Example 8 to 11 isshown in FIG. 20. In this FIG. 20, as in FIGS. 11 and 16, plots at bothends of each line segment represent chromaticity coordinates of lightfrom the green light emitting section and the red light emitting sectionin each example. FIG. 21 shows the emission spectrum, as calculated inthis example.

The entire luminous flux from the white light was 1.3 lm per one blueLED.

Example 9

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.27, 0.39).

Further, the red light emitting section was prepared in the same methodas described for Example 8, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.43, 0.24).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.47:0.53. FIG. 22 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.3 lm per one blueLED.

Example 10

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.28, 0.42).

Further, the red light emitting section was prepared in the same methodas described for Example 8, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.40, 0.22).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.46:0.54. FIG. 23 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.4 lm per one blueLED.

Example 11

The green light emitting section was prepared in the same method asdescribed for Example 1, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.30, 0.47).

Further, the red light emitting section was prepared in the same methodas described for Example 8, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.36, 0.20).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.45:0.55. FIG. 24 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.4 lm per one blueLED.

Example 12

The green light emitting section was prepared in the same method asdescribed for Example 5, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.24, 0.36).

Further, the red light emitting section was prepared in the same methodas described for Example 1, except thatCa_(0.1984)Sr_(0.7936)Eu_(0.008)AlSiN₃ was used as the luminescentmaterial of red light emitting section and the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.48, 0.27).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.52:0.48. Further, a chromaticity diagramillustrating the method of generating white light in Example 12 to 14 isshown in FIG. 25. In this FIG. 25, as in FIGS. 11, 16 and 20, plots atboth ends of each line segment represent chromaticity coordinates oflight from the green light emitting section and the red light emittingsection in each example. FIG. 26 shows the emission spectrum, ascalculated in this example.

The entire luminous flux from the white light was 1.1 lm per one blueLED.

Example 13

The green light emitting section was prepared in the same method asdescribed for Example 5, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.26, 0.42).

Further, the red light emitting section was prepared in the same methodas described for Example 12, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.42, 0.24).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.51:0.49. FIG. 27 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.1 lm per one blueLED.

Example 14

The green light emitting section was prepared in the same method asdescribed for Example 5, except that the mixing ratio of the luminescentmaterial and the binder was adjusted so that the mixed light (shortwavelength light) consisting of blue light and green light gives achromaticity coordinate of (x, y)=(0.27, 0.45).

Further, the red light emitting section was prepared in the same methodas described for Example 12, except that the mixing ratio of theluminescent material and the binder was adjusted so that the mixed light(long wavelength light) consisting of blue light and red light gives achromaticity coordinate of (x, y)=(0.40, 0.22).

White light was generated similarly to Example 1 and the emissionspectrum was calculated. In this example, spectral ratio of the lightfrom the green light emitting section and that from the red lightemitting section was set at 0.52:0.48. FIG. 28 shows the emissionspectrum, as calculated in this example.

The entire luminous flux from the white light was 1.1 lm per one blueLED.

SUMMARY

From the examples mentioned above, it was confirmed that white lightwith abundant luminous flux can be obtained with the green lightemitting section and red light emitting section installed independently.Further, this white light contains blue light, green light and red lightcomponents, and the use of a backlight unit comprising independentlyinstalled green light emitting section and red light emitting section,as described above, makes possible the creation of a display devicehaving high emission efficiency and color reproduction property.

INDUSTRIAL APPLICABILITY

The present invention can be applied in any field where light isinvolved. The examples include: lighting system used indoors as well asoutdoors, cellular phone, electric appliances for household use, displayto be installed outdoors, display for various electronic appliances suchas liquid crystal display and liquid crystal projector, indoorsindicator.

Although the present invention was explained in detail referring tocertain embodiments, it is evident for those skilled in the art thatvarious changes or modifications can be made thereto without departingfrom the spirit and scope of the present invention.

The present invention is based on the specification of Japanese PatentApplication No. 2004-194154 filed on Jun. 30, 2004, and thespecification of Japanese Patent Application No. 2004-303363 filed onOct. 18, 2004, and their entireties are hereby included by reference.

1. A method for adjusting the color of white light and emitting thewhite light, the method comprising: preparing a first blue light source,a first luminescent material that is excited by a first blue lightemitted by the first blue light source and thereby emits green light, asecond blue light source, and a second luminescent material that isexcited by a second blue light emitted by the second blue light sourceand thereby emits red light; generating the white light through mixingthe first blue light emitted by the first blue light source, the greenlight emitted by the first luminescent material, the second blue lightemitted by the second blue light source, and the red light emitted bythe second luminescent material; and adjusting a balance in intensity ofthe first and second blue lights, green light, and red light containedin the white light by adjusting a ratio of electric power supplied tothe first blue light source and electric power supplied to the secondblue light source.
 2. The method according to claim 1, wherein theadjusting of the ratio of electric power comprises adjusting a ratio ofa value of an electric current supplied to the first blue light sourceand a value of an electric current supplied to the second blue lightsource.
 3. The method according to claim 1, wherein: the first bluelight source and the second blue light source are driven by electricpulses; and the adjusting of the ratio of electric power comprisesadjusting a ratio of a pulse lighting period of the first blue lightsource and a pulse lighting period of the second blue light source. 4.The method according to claim 1, wherein: the first blue light source isa light emitting diode, laser diode, or an electroluminescence element;and the second blue light source is a light emitting diode, a laserdiode, or an electroluminescence element.
 5. The method according toclaim 1, wherein the second luminescent material is a phosphorrepresented by following Formula (3),M_(a)A_(b)D_(c)E_(d)X_(e)   (3) where M represents one or more elementscontaining at least Eu and selected from the group consisting of Mn, Ce,Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb, A represents one or moreelements selected from bivalent metal elements other than M, Drepresents one or more elements selected from tetravalent metalelements, E represents one or more elements selected from trivalentmetal elements, X represents one or more elements selected from a groupconsisting of O, N, and F, and a value of a, b, c, d, e is selected fromthe value satisfying all of the following conditions: a is a number of0.00001≦a≦0.1 a and b establish a relationship of a+b=1 c is a number of0.5≦c≦4 d is a number of 0.5≦d≦8 c, d, and e establish relationship of0.8×(2/3+4/3×c+d)≦e, and c, d, and e establish relationship ofe≦1.2×(2/3+4/3×c+d)
 6. A light emitting device, comprising: a firstlight emitting section that comprises a first blue light source and afirst luminescent material which is excited by a first blue lightemitted by the first blue light source and thereby emits green light,and the first light emitting section emits a first mixed lightcontaining the first blue light emitted from the first blue light sourceand the green light emitted from the first luminescent material; and asecond light emitting section that comprises a second blue light sourceand a second luminescent material which is excited by a second bluelight emitted by the second blue light source and thereby emits redlight, and the second light emitting section emits a second mixed lightcontaining the second blue light emitted from the second blue lightsource and the red light emitted from the second luminescent material,wherein the light emitting device emits white light containing the firstmixed light and the second mixed light, and when a ratio of electricpower supplied to the first blue light source and electric powersupplied to the second blue light source is changed, balance inintensity of the first and second blue lights, green light, and redlight contained in the white light changes.
 7. The light emitting deviceaccording to claim 6, wherein: the first blue light source is a lightemitting diode, a laser diode, or an electroluminescence element; andthe second blue light source is a light emitting diode, a laser diode,or an electroluminescence element.
 8. The light emitting deviceaccording to claim 6, wherein the first light emitting section furthercomprises a third luminescent material which is excited by the firstblue light emitted by the first blue light source and thereby emits redlight.
 9. The light emitting device according to claim 6, wherein thesecond light emitting section comprises a fourth luminescent materialwhich is excited by the second blue light emitted by the second bluelight source and thereby emits green light.
 10. The light emittingdevice according to claim 6, wherein the second luminescent material isa phosphor represented by following Formula (3),M_(a)A_(b)D_(c)E_(d)X_(e)   (3) where M represents one or more elementscontaining at least Eu and selected from the group consisting of Mn, Ce,Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb, A represents one or moreelements selected from bivalent metal elements other than M, Drepresents one or more elements selected from tetravalent metalelements, E represents one or more elements selected from trivalentmetal elements, X represents one or more elements selected from a groupconsisting of O, N, and F, and a value of a, b, c, d, e is selected fromthe value satisfying all of the following conditions: a is a number of0.00001≦a≦0.1 a and b establish a relationship of a+b=1 c is a number of0.5≦c≦4 d is a number of 0.5≦d≦8 c, d, and e establish relationship of0.8×(2/3+4/3×c+d)e, and c, d, and e establish relationship ofe≦1.2×(2/3+4/3×c+d).
 11. The light emitting device according to claim 6,wherein: the first light emitting section is formed in a firstcup-shaped recess; the second light emitting section is formed in asecond cup-shaped recess; the first cup-shaped recess is formed in afirst frame; and the second cup-shaped recess is formed in a secondframe different from the first frame.
 12. A light emitting device,comprising: a first light emitting section that comprises a first lightsource and a first luminescent material which is excited by lightemitted by the first light source and thereby emits light containing alight component having a wavelength longer than that of the lightemitted by the first light source, and the first light emitting sectionemits a first light containing the light emitted from the firstluminescent material; and a second light emitting section that comprisesa second light source, and a second luminescent material which isexcited by light emitted by the second light source and thereby emitslight containing a light component having a wavelength longer than thatof light emitted by the first luminescent material, and the second lightemitting section emits a second light containing the light emitted fromthe second luminescent material and being different in chromaticity fromthe first light, wherein the light emitting device emits mixed lightcontaining the first light and the second light, and when a ratio ofelectric power supplied to the first light source and electric powersupplied to the second light source is changed, chromaticity of themixed light changes.
 13. The light emitting device according to claim12, wherein: the first light source and the second light source aredriven by electric pulses; and the change in the ratio of electric powerincludes a change in a ratio of a pulse lighting period of the firstlight source and a pulse lighting period of the second light source. 14.The light emitting device according to claim 12, wherein: the firstlight source is a light emitting diode, a laser diode, or anelectroluminescence element; and the second light source is a lightemitting diode, a laser diode, or an electroluminescence element. 15.The light emitting device according to claim 12, wherein: the lightemitted by the second light source has a wavelength of 370 nm or longerand of 500 nm or shorter; the second luminescent material is a phosphorrepresented by following Formula (3),M_(a)A_(b)D_(c)E_(d)X_(e)   (3) where M represents one or more elementscontaining at least Eu and selected from the group consisting of Mn, Ce,Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm and Yb, A represents one or moreelements selected from bivalent metal elements other than M, Drepresents one or more elements selected from tetravalent metalelements, E represents one or more elements selected from trivalentmetal elements, X represents one or more elements selected from a groupconsisting of O, N, and F, and a value of a, b, c, d, e is selected fromthe value satisfying all of the following conditions: a is a number of0.00001≦a≦0.1 a and b establish a relationship of a+b=1 c is a number of0.5≦c≦4 d is a number of 0.5≦d≦8 c, d, and e establish relationship of0.8×(2/3+4/3×c+d)e, and c, d, and e establish relationship ofe≦1.2×(2/3+4/3×c+d).
 16. The light emitting device according to claim12, wherein: the first light emitting section is formed in a firstcup-shaped recess; the second light emitting section is formed in asecond cup-shaped recess; the first cup-shaped recess is formed in afirst frame; and the second cup-shaped recess is formed in a secondframe different from the first frame.
 17. A light emitting device,comprising: a first light emitting section that emits a first mixedlight which contains blue light and green light and which has a firstpredetermined chromaticity; and a second light emitting section whichemits a second mixed light which contains blue light and red light andwhich has a second predetermined chromaticity different from the firstpredetermined chromaticity, wherein the light emitting device emitswhite light having a chromaticity coordinate on a line segmentconnecting a chromaticity coordinate of the first mixed light and thatof the second mixed light.
 18. The light emitting device according toclaim 17, wherein the chromaticity coordinate of the first mixed lightis in the range surrounded by (0.25, 0.65), (0.43, 0.52), (0.32, 0.33),and (0.18, 0.33).
 19. A method for producing an intended colored whitelight, the method comprising: a step for producing a first mixed lightcontaining a first blue light and green light, by using a first bluelight source which emits the first blue light and a first luminescentmaterial which is exited by the first blue light emitted by the firstblue light source and thereby emits the green light; a step forproducing a second mixed light containing a second blue light and redlight and being different in chromaticity from the first mixed light, byusing a second blue light source which emits the second blue light and asecond luminescent material which is exited by the second blue lightemitted by the second blue light source and thereby emits the red light;a step for mixing the first mixed light and the second mixed light toproduce a white light containing the first and second blue lights, greenlight and red light; and a step for adjusting a balance in intensity ofthe first and second blue lights, green light and red light contained inthe white light.
 20. The method according to claim 19, wherein the firstlight source is alight emitting diode, a laser diode, or anelectroluminescence element; and the second light source is a lightemitting diode, a laser diode, or an electroluminescence element. 21.The method according to claim 20, wherein the adjusting step comprisesadjusting a ratio of electric power supplied to the first blue lightsource and electric power supplied to the second blue light source.